From AJCO: The ghost of Mercy, a bandit slaughtered by Curls some years prior, tries to hide the fact that he has an Oh, Crap! moment when Kaja shows up — Kaja being a powerful angel with the power to exorcise him from the body of the helpless girl he'd possessed without hurting her (therefore making his threats to jump off the tower meaningless). He eventually accepts his fate.
During the last bit of the Silent Hill: Dying Inside review, the second Pyramid Head of all beings jerks back in fright upon seeing Linkara's new weapon.
Linksano: Oh no... He's coming....HE'S COMING!
The look on Mechakara's face when he hears Linkara coming home in the middle of his You Bastard! rant.
The Twilight Zone #9 — The Entity has taken Pollo.
Silent Hill: Paint it Black — Now Spoony's gone.
Silent Hill: Among the Damned — So is Marzgurl!
Silent Hill: The Grinning Man — And so is Benzaie, Sad Panda, and about half of the French population...
Spider Man: Planet of the Symbiotes — Angry Joe, JewWario, Dr. Insano...hell, pretty much everybody in the world except Linkara and '90s Kid...who turns out to be the Entity in '90s Kid's form...
All-Star Batman and Robin #6 — Linkara goes very still when Nimue, controlling AI of the universe's most powerful warship, implies that she might be losing her mind.
Spider-Man: Crossfire — "Your computer is dead, Champion. Tell me...are you afraid?"
The episode for Giant Monster Gamera opens with him yelling "Oh, shit!" upon learning that the Patreon goal for a Gamera-a-thon has been reached.
In Break Quest Club, the town in "Con-Voy" utterly panics when Magnus and Freya, the party's escorted merchants, roll up. It turns out this is because they're infamous bandits and robbers.
Can You Spare a Quarter?: Despite Graham's attempts at softening the impact of the revelation, when he tells Jamie that the boy has been hitting him during his nightmares Jamie freaks out out of fear that Graham will beat him up like his father used to and runs away.
The Cockroach Metamorphosis has Thoth wrestling with a Nyarlathotep in bear form (in free-fall!) only for the both of them to come to the realization that they are currently fighting inside an even bigger god, and as they try to sneak out without waking it up, they turn around to see an ominous pair of eyes staring right at them. Even The Crawling Chaos himself flips his shit in panic.
First there's the narrator's reaction when she sees a face in the photograph she took of the crawlspace.
Then the narrator has an even bigger one when she hears the creature coming towards their bedroom and realises Stephanie forgot to bolt the door after using the bathroom.
Critical Role (Campaign 1): And entire-group one when Matt informs them that Keyleth's Wind Walk spell (which she'd been gleefully excited about casting), prevents them all from attacking for at least ten rounds.
Travis gets one when, after successfully talking the other players out of going to confront Grog's abusive uncle, the party travel to a completely different city instead and discover it overtaken by a tribe of bandits...led by Grog's family. He even drops out of character on realising it, a near-unforeseen occurrence.
In "im outside", Daisy rambles on for a few minutes until she realizes Strawberry is still in the house with Alan, at which point she cuts herself off and ends the video.
In the sixth episode of DesuDesBrigade's Pocky Spot, Arkada gets precisely this after hearing the Professor Otaku has to a little tidbit of info dropped.
Nova had one when Sparks was smashed to the ground by a brainwashed Metal Tyrannomon.
Mana got one after said Metal Tyrannomon Digivolved to Rust Tyrannomon despite the odds still being in her favor along with everyone else that was fighting the aforementioned Mega.
Nova had another one when he saw that the nightmare from previous night was starting to come true when Sparks went wild for the first time while using his new Hunter Sparkmon form along with the two Sealsdramon mercs Sparks and Jimmy were facing, despite their expressionless faces. If they didn't have that look then, they definitely got it when Nova threatened to sic Hunter Sparkmon on them again.
Nova got one in each of his following nightmares, but only one of those nightmares were onscreen so far.
Dr. Horrible's Sing-Along Blog: When his freeze ray powers down, Dr. Horrible has just enough time to note "That's not a good sound..." before his face gets introduced to the now-free Captain Hammer's fist. Again.
Earthquake & the G20 by Matt Santoro ends with an earthquake, causing Matt to panic.
Game Grumps: When Arin decided to cue up Sonic the Hedgehog (2006), the first thing out of anyone's mouth was Jon simply saying "Oh no. Oh no." when he recognizes the menu.
While playing Escape the Ayuwoki, Jacksepticeye ends up being repeatedly killed by the titular monster. Eventually he hides in a closet, but while he's talking the Ayuwoki continuously sweeps by his hiding place. Jack then comes to a realization.
Every microwave show at one point or another has one of these episodes.
Is It a Good Idea to Microwave This? most famously has the airbag episode and to a lesser extent the second lava lamp episode. In the first one, Jory was literally SECONDS from being killed. The reaction afterwards is priceless. However, that wasn't their first "oh crap" moment, in Season 6 when trying to put out a fire from a singing pen, the battery explodes and Jory is surprised he doesn't lose his hand. The exploding rubbing alcohol episode may also qualify due to their reaction of genuine fear. The dynamite, propane tank, gasoline, and other similar episodes are NOT this because they KNOW of the danger potential.
In a sense their microwaving a microwave episode qualifies since that was the first time they broke a microwave that wasn't at the end of a season, and so they were unprepared for it. The latter half of the season isn't even filmed until it's almost time to air the microwave a microwave episode.
dOvetastic Microwave Theater rarely has these since dOvetastic takes TONS of precautions, the closest example to this trope being the propane tank, which he actually gets to explode on its own (Jon and Jory used gasoline and fireworks to get it to blow up) and possibly the dry ice bomb specials. The videos that DO qualify for this, however, are not his microwave videos but things like where he saws into a propane tank or any high voltage cooking episode with anything explosive involved. The deck varnish and CO2 cartridge special applies too since the cartridges launch over 100 feet.
What Happens When You Microwave This? has a few notable episodes, but the only true Oh, Crap! moment happened with a lava lamp since they weren't expecting it to blow up like that. The bag of popcorn for 35 minutes is a bit of an ironic result since they thought it broke their microwave after burning for so long. The cameraman thought it was hilarious that after doing so many dangerous things, it may have been popcorn that broke the microwave.
Microwave Me has had very few incidents like this since the creator always seems prepared for the result, even treating a butane lighter with a bit of healthy respect, but the one that sticks out is the champagne bottle. Apparently he thought Brainiac faked their explosion (due to some highly unlikely experiments like the Newton's Cradle episode and admitted fakery of their alkali metals in a bathtub experiment) and that the bottle would only take the door off the microwave. What actually happened was an explosion very similar to the Brainiac episode with the door being launched quite a distance (in three pieces to boot), the microwave being ripped almost in half, the turndial ripped nearly off of the microwave, and the explosion was supposedly as loud as a large firework mortar going off, like one would see at a professional display.
Smaller microwave shows rarely get this, but you do see this occasionally when they only have one microwave on hand and their experiment unexpectedly wipes it out. Most notably Jzizzle 77 who microwaved high profile things like CO2 cartridges, aerosol cans, road flares, model rocket engines, and even a mini-printer. His experiment microwave broke after the mini-printer.
At the end of a very angry confrontation with Darcy, Lizzie tells him to watch her videos, referring to her video diary: the video diary in which she has spent a significant amount of time mocking, criticizing, and insulting him. On the Internet.
Lizzie: He could sue me for some of the stuff I've said about him — (to camera) not that it's untrue! He's a really successful businessman. Really successful businessmen sue people, a lot. So I'm told. Oh god, do we know any lawyers?
Logan's Tale: Logan's reaction to the Platinum Chip delivery order, particularly the clause about mercenary reclamation teams hunting him down if he fails to deliver.
Mahu: In "Second Chance" this is the reaction of all of the forces of the Commonwealth as they land on the sentient planet of "Voice". After weeks of constant bombardment, they deploy in several waves what is the largest army the nation has ever deployed. The garrison of drone defenders is cut down quite easily...and then, absolute chaos ensues.
Probably the biggest example of this has to be Jay revealing he did not post Entry ######.
Entry #26. "When did we get a camera?" Though it's not particularly apparent on-screen, you can tell Alex has just realized "okay, this is really, really bad".
Markiplier's Let's Play of Five Nights at Freddy's 4 has one in Part 5 when he witnesses The Bite of '87. He starts to reach that bit when He reads the part where the main character's brother and his gang brings him to the Fredbear animatronic and visibly flinches when it happens, rendering him with Stunned Silence for a good ten seconds.
The reaction of people in Mighty God King's version of Marvel's Civil War storyline when Thor shows up.
A hilarious one happened in the Let's Play Grand Theft Auto V episode "Path To Insanity" where Ryan's killstreak is ended by Ray riding in a tank. Ryan is minding his own business, killing people as he attempts to raise his insanity meter when Ray casually strolls up in a tank on the street.. Ryan's reaction:
Ryan:OH, SHIT!Ray's in a tank!
Another happens in the CarDunkEn episode when Geoff accidentally fires a rocket at Jack's Cargobob, saying "Oops!" a split second before the rocket hits Jack.
Mini Drivers, a Formula One cartoon, often exaggerates the various driving styles, quirks, etc. of the drivers in the series. So in this 2012 postseason video, two very crash-prone drivers (Pastor Maldonado and Romain Grosjean) start on the front row of a race, which immediately makes Mini-Girl (the starter) nervous. Once the field takes the green, every driver behind them Oh Craps when they realize the two are about to start a crash that, if the "achievement" is to be believed, will rival the alleged Mayan apocalypse.
The title character of My Name Is Zytherys only considers it a bit odd when a mysterious journal shows up on her doorstep. Slightly more odd when it begins to fill itself with her own handwriting. However, when her laptop begins to show visual tearing and starts scrolling on its own...
Briefly discussed in Red Letter Media's Half in the Bag episode on Godzilla vs Kong. Mike is unaware of the trope's name and suggests creating a new trope. They suggest they call it the "Firestien Effect" after Harvey Firestien's use in Independence's Day.
During the RP of The Marios, this is the trio's general reaction when the creator of the bad LP in question, LuwiigiMaster, disses Retsupurae during his LP. Diabetus later comments that he should pre-screen LPs before bringing the gang over to riff them. If one reads the comments, the guy apparently was trying to purposely make a So Bad, It's Good video just to get RPed. Made even more hilarious due to their depiction of said LPer as part of The Mafia.
Search for Sandvich: In "Out to Sea!", the mercs react with horror when they discover that the Giggling Secretary left the remains of an eaten sandwich on her plate.
Cody Jenson does this at the end of V1. He finishes off Sidney Crosby, who attacked him to save Adam Dodd, and then turns around just in time to see a very angry Adam Dodd attacking him with a katana. A quick 'Oh crap!' moment, considering that he gets stabbed and impaled almost immediately.
Also happens to Harry Tsai in V3, when he sees Andrea Vanlandingham's detached collar, whom he killed earlier in the game, moments before Denise Dupuis wreaks her vengeance upon him.
In his Top 11 F*ck Ups special, The Nostalgia Critic decides to hunt down Douchy McNitpick. Douchy is confident that there's no way the NC will find him, until he hears a window in his house breaking.
In Demo Reel, Donnie has an amusing "ah fuck it's happened again" expression and groan when Egoraptor is in the bed next to him instead of Uncle Yo.
Critic's reaction to Hyper looking for him is to usually hide behind a chair or duck behind the couch.
In Thalia's Musings, this is Thalia and Apollo's reaction when Eros (falsely) tells them that he's dosed them with a love potion.
In "Wishing Hell", an early episode of The Thrilling Adventure Hour's "Beyond Belief" segment, Frank and Sadie Doyle face off against Nightmares the Clown for the first time. In trying to frighten Sadie, who otherwise is unable to take him seriously because she finds clowns hilarious, he assumes his true form of a giant spider. Sadie then notes she's not afraid of giant spiders, but begs him not to turn into a normal, tiny spider, which she does fear. Nightmares does so, but does not realize until Frank's shoe starts to come down on him that Sadie was Briar Patching him.
Sadie: A spider! Spider, Frank! Frank: Yes, I see it, love. Let me get rid of it for you. Nightmares: No! Wait! *squish*
Tobuscus' Let's Plays are littered with this type of commentary, most often phrased as some variant of, "I'm screwed I'm screwed I'm gonna die I'm gonna die I'm dead I'm dead GOD DANGIT!"
Nearly every Let's Play of The Witch's House on the internet causes the player to have moments like these, as traps are easy to fall into. The amount of time that the player has to realize how screwed they are varies from trap to trap. PewDiePie's playthrough is a good example, as is this one.
In Worm, Tattletale gets one when she realizes that Scion is the one who will destroy the world.
During her Worms Armageddon matches with her friends, Pink Kitty Rose panics whenever someone breaks out a Banana Bomb or Armageddon. This reaches its peak during a melee-centric match when, on the first turn of the game, Cutman Mike obtains Armageddon via a Crate Shower and unleashes it immediately.
At the very end, when our long-suffering protagonist has finally reached the Big Bad, only to discover that it's what has been guiding him through every last acre of hell, this entire time.
, Daisy rambles on for a few minutes until she realizes Strawberry is still in the house with Alan, at which point she cuts herself off and ends the video.