After awhile in 8-Bit Theater, Sarda gets tired of the games and decides to just outright torment the Light Warriors until the end of time, made worse by absorbing Black Mage's evil side.And then came Chaos...
At the end of Falst's intro arc, after Doctor Jolon is defeated, he starts begging and pleading, desperately making a rather pathetic last-ditch effort to manipulate his way out of the situation.
Right after Alinua and Falst break open the mountain prison in Zuurith, the Arenamaster loses his temper over everything that's happened and threatens Falst, yelling that he has not yet lost control.
In Darths & Droids, Boba Fett is out on a quest of vengeance against Obi-Wan Kenobi. When he finally hears that Obi-Wan is already dead, he freaks out about how he's been wasting his life and how he can't get his revenge. This is exactly why the heroes didn't tell him before, by the way. He then flies into a wall, falls into the Sarlacc and dies.
Dragon Ball Multiverse: U4 Zen Buu goes berserk when Vegetto is eliminated from the tournament by XXI's magic and XXI refuses a rematch.
Sarv'swati Vel'Sharen watched her rule crumple around her. Her hold on the city of Chel toppled before her eyes, as the Val'Sarghress rushed through her streets, killing her army and children and pressing ever close to the total destruction of her line. She started slipping deeper and deeper into desperation, her soldiers conducting more guerrilla tactics and Sarv'swati eventually hiring an entire army of raiders, allowing them to enslave and raid her city in return for their services. As she faces her final defeat at the hands of the Sarg's and is forced to flee to the site of her mother's murder at her hands, she breaks down, screaming in horror and curling up to say how sorry she is and how she wishes her mother would come back. Sarv'swati is a centuries-old ruthless dictator, now begging for her mommy.
Unbelievably, Snadhya'Rune is a haemophobic (has a fear of blood). After a really smart Sarghress stabs her in the back, she proceeds to murder everyone in a fifty-foot radius. And then mellows out like nothing happened. Her girlfriend finds it somewhat disturbing.
Damien of El Goonish Shive has an absolutely EPIC breakdown when, during his battle with Omega Grace, he realizes that he was very likely created in a lab like Grace and her "brothers" (as opposed to his initial belief that he was a god that was summoned to this world), and ends up self-destructing in an attempt to kill Grace.
Even more epic since he saw this as a twisted win/win. If he was a god, he would survive. If he wasn't, he didn't want to.
Dr Merlot seems to take news of Miss Clay's true identity rather badly.
While his breakdown was just very hammy, Zola suffers the most dangerous variation. After she forfeits her chance to escape for another attempt to kill Agatha and fails, she takes a beating and it looks like she will be defeated rather anticlimactically. Then she decides that it is better to die with her foes than to lose, downs a vial of Psycho Serum and goes on a murderous rampage.
The newly super-charged Lord Snackford chooses a very bad time to launch into a Sparky rant about his plans being thwarted, giving a Genre Savvy opponent the perfect opportunity to toss him into a closing dimensional gateway.
In The Inexplicable Adventures of Bob!, the first time Bob beats Fructose Riboflavin, Riboflavin is disappointed but takes the defeat fairly gracefully. The second time, though, he collapses in tears, sobbing that he's been trying to conquer the Empire for centuries and he just can't do it— and Bob proves himself a nice guy by trying to cheer the villain up. And the third time they meet, Bob vivisects Riboflavin's personal Jerk Justifications (politely, of course), making it clear that all his crimes have been pointless, and Riboflavin explodes in rage, frantically chases after Bob, and ultimately beats him up severely.
In It's Walky!, Sal has a series of these after the appointment of Linda Walkerton as the head of SEMME drives her to make a Face–Heel Turn. This culminates in what amounts to a Villainous BSOD when her attempt to blow up the world using the Power Booster Rod is interrupted by the arrival of Danny, the only person left that she has enough feelings for to not be psychotic enough to kill. Prior to that, Sal's Villainous Breakdowns tended to not immediately proceed her capture because she is super-strong, and so even thrashing about in a blind rage, she tends to beat people.
There are at least two characters from Kid Radd who seem to be likely candidates for this treatment, but the ultimate breakdown goes to somebody else. The Seer does not take holes in its omniscience very well. Not well at all.
Garou has one of these after being defeated by Saitama in One-Punch Man.
Start of Darkness spoiler: Xykon also loses it shortly after turning into a lich, when he realizes that he can't taste coffee anymore.
Tarquin begins to lose it when seeing that his son Elan is quite happy being the support for his team instead of trying to be the leader. And just in general for being treated as some second-rate Arc Villain when he believes himself to be the Big Bad, refusing to admit that that particular title belongs to Xykon.
Tarquin: *to the Order at large* What the hell is wrong with you? How did you all get to such a high level without anyone teaching you your place?
After that, he only continues to further lose his cool, threatening to kill absolutely everyone Elan knows and cut off his hand, right until he's given a short talk while hanging off an airship, and left to drop into the desert. He survives the fall physically, but mentally might be another matter...
Elan, this isn't over yet! Where's the growth? You didn't lose anything! Nothing has changed! ELAN, YOU COME BACK HERE AND GIVE THIS PLOTLINE A SATISFYING RESOLUTION THIS INSTANT!!
....ELAN! THERE'S NO SENSE OF CLOSURE! I DON'T KNOW WHAT HAPPENS NEXT!
THIS IS A TERRIBLE ENDING!!!
Once Hel's vampirical clerics are almost entirely exterminated, and her ultimate plot that needed them is thus dashed, she has a big one. She gets her corpse-like Game Face on, furiously rants at Loki (her own dad), threatens him with oblivion and works herself up into such a big fury she nearly passes out (and briefly flickers out of existence, as her belief stocks are running thin).
Once this world crumbles, I will be free of your wretched wager forever. Free to empower my own living clerics, and as my first commandment, I will task them with slaughtering your followers in hideous ways wherever they lurk. You will waste away and DIE as your name is erased from every history book. Now get out of my domain!
In the Sluggy Freelance story arc "That Which Redeems", Horribus becomes increasingly obsessed with catching Torg as the story progresses, to the point of jeopardizing his invasion of another world. By the end of the story, Horribus is curled up in the fetal position, gibbering about how Torg's behind everything wrong in his life.
First Advisor Devon Woodgrove in S.S.D.D. first becomes exceedingly angry, then quite calm, and then a teensy bit unhinged. It doesn't help one whit that the Oracle, King Arthur, and probably others are each exploiting this for their own benefits.
Bonnie: WAIT ONE GODDAMN SECOND, YOU CUNTS! I DID NOT DO THIS FUCKING FAKE ACT FOR 39 DAYS JUST TO GET FUCKED OVER BY A JURY FULL OF GODDAMN BITTER BITCHES! I WAS THE ONLY PERSON PLAYING THIS FUCKING GAME ALL SEASON! AND I BETTER GET MY GODDAMN MONEY! I CONTROLLED FUCKING EVERYONE! I WAS THE MASTERMIND! I DID EVERYTHING! THIS WAS ALL ME; YOU BETTER GIVE ME WHAT I FUCKING DESERVE!
Jeff Probst: Well, I'm glad you think that. Because the jury seems very eager to ask you some questions.
Bonnie has another one in Season 16, breaking down with a similar rage-filled rant after her tribemates completely rip apart her disguise and then flipping the double bird to everyone and storming out before Jeff can finish reading the votes.
Desmond in Season 14 was smugly calm and self-assured of his eventual victory for the entire season, until Liz and Jojo made it clear to him that neither of them planned to take him to the finals and that they had pulled a Twin Switch on him that he had been completely blind to. Cue him breaking down into a screaming tirade about how Liz played without moral principles, despite him having played in much dirtier fashion himself.
Tower of God: Hoh. Resulted in a suicide and a reason you suck speech.
As he's told that Ana and Toby are planning to run off together Stockyard sits in his office staring at the floor with tears streaming down his face, in contrast to his usual devil may care swashbuckling attitude. Later that night he kills Toby, his closest friend and ends up dying screaming and crying himself when the silver, which he's not had much mind for given his distraction, possesses Toby and attacks him.
As the situation in Port Morstorben deteriorates and the usually suave smarmy Karl realizes just how expendable he is, he freaks out badly enough to try and assassinate Queen Sonorie personally, while she's surrounded by her soldiers and retainers. He's dragged off to prison, shrieking in terror the whole way.
when she discovers she can't create a race of perfect slave children with her Mix and Match Critter of a boyfriend.