Try to say that anime is the same as cartoons to a group of anime fans. Go ahead, see what happens. This has become much less common nowdays, however.
If you grew up with 4Kids Entertainment or other dubs that change the setting to the United States, don't ever think that these series were made in America unless you're prepared to be attacked by an angry mob. Doesn't help that back then, networks would always clump their anime among their Western cartoons, and not refer to it as such. Like the above, however, it's become far less common as anime has become more well-known and mainstream.
Do not refer to an ecchi work as a hentai work, given the differences between the two types of works, art styles, and situations within the works. For example, So, I Can't Play H! is ecchi, not hentai.note There are some exceptions, anime such Joshiochi! 2-kai kara Onnanoko ga... Futtekita!?, Princess Lover!, Uwakoi, Aki Sora and Yosuga no Sora sort of swing between the lines of hentai and ecchi (the first one has both +15 version on AT-X that is ecchi and +18 version that is hentai, second one is an ecchi anime with hentai OVA and the rest have actual sex scenes, just without genitalia). Still, those are exceptions, not a rule.
This also goes for vice-versa, for instance Itadaki Seieki is hentai, not ecchi.
Unironically claiming that anime is an art-style instead of animation from Japan will usually result in a Flame War.
When it comes to anime and manga characters that have western-origin names (ex: Thomas, Joseph, Edward, etc.), always spell and pronounce them the English way, not the Japanese way (ex: if a character's name is "Joseph", don't spell it as "Josefu").
While Hayao Miyazaki is Studio Ghibli's most prolific director, you'll be wise to not mistake the studio's non-Miyazaki films (such as the films of Isao Takahata) for Miyazaki's unless you want to anger Ghibli fans.
Even though Animesque Chinese donghua do appear in several anime websites, its best not to refer them as anime, at least due to the country of origin.
Mecha fans are not fond of people making claims such as "Unlike other mecha shows, [insert show here] focuses on the characters" due to the fact that it blatantly ignores prior works. Stating as such is liable to cause said Mecha Fans to declare you a bandwagoner.
Specific anime
The proper way to pronounce AKIRA is "AH-kee-rah". Do NOT pronounce it "uh-KEE-rah" or "uh-KAI-rah" unless you want to get on the fandom's bad side.
Alleging that Attack on Titan is antisemitic due to the parallels between Eldians and Jews will earn you angry fans (especially those who are of Jewish descent) reminding you that the series portrays the oppression of the Eldians as a bad thing.
IT'S NOT "GATSU/GATTS"! IT'S "GUTS"! Since the official releases (both manga and anime) are widely considered to have good translations, fans who came into the series through shoddy scanlations are typically looked down upon for using incorrect character names.
Don't call Berserk a Shōnen, it's a Seinen, fans will shred you.
Black★Rock Shooter: Mistaking the title character for a recolored Hatsune Miku. This one is a mess, because BRS was created independently of Miku, but their coincidental similar appearances led to the creation of a BRS-themed Miku song by a famous producer, which was the Colbert Bump that got the franchise going. Besides that song, they are not related; but people still get them confused for obvious reasons, and the fans of both franchises get pretty annoyed when it happens.
Though she was initially called "Dark Chii" by fans due to No Name Given for a large part of the manga, call Freya that to any Chobits fan's face and feel the wrath of the heavens descend upon you since it's basically admitting that you either haven't gotten through the entire series yet or didn't bother to finish it, as her true identity and The Reveal of it make up the story's climax.
Cyberpunk: Edgerunners: Similar to the Uzaki-chan example below, don't call Rebecca a child. She's actually 20 years old and is in fact older than the main character, David.
Tell any fan that Digimon is a rip-off of Pokemon and you'll likely be torn apart. Same goes for Yo-kai Watch and every other Mon franchise, but as Digimon is the oldest V-Pet/Mon genre-fusion, and arguably the second biggest franchise in both of those genres, that mistake is second only to calling genre founder Shin Megami Tensei a Pokémon rip-off. (Ironically, due to the collapse of V-Pets in The West the Digimon franchise has arguably started emulating Shin Megami Tensei more than it ever did Pokémon...)
Arale is pronounced "ah-rah-leh", not "ah-rail-lee" or "ah-ral" with a silent "e".
Akira Toriyama wasn't unknown until Dragon Ball: he'd already been doing Dr. Slump for four years to high praise in Japan, meaning he was a household name before it even began (which goes to show how astronomical Dragon Ball was).
A great, great many if you're aware of the original Japanese version compared to Funimation's dubs. Dragon Ball isn't an irrelevant prequel to Dragon Ball Z where the story "truly" begins, Goku is not an inherently superheroic character and the "light of the universe", and Dragon Ball was in no way a flop until it was brought to Toonami, among a great many others.
Lunch is not a Saiyan. She is a human with dissociative identity disorder.
Krillin and Tien are humans. Never, ever say they are aliens.
Akira Toriyama did not consider ending the story at Namek or Cell and continued the story due to fan demand.
The Funimation cast are not the only people to have played the characters in English; this leaves out at least the cast hired by Ocean Productions, among others.
Don't spell Dragon Ball Z as "Dragon Ballz".
Don't state that the Z in Dragon Ball Z exists because someone meant to write 2 and it looked like the letter Z. It exists because Toei wanted to rebrand the anime for the upcoming tone shift, and Toriyama suggested the Z because he thought his manga would be ending soon.
Dr. STONE reboot: Byakuya is not canon to Dr. STONE. Claiming that Senku and friends will get to meet Rei in space is a good way to annoy the fans. Anyway, Reboot's canon has already been blatantly contradicted by Senku visiting Europe and reviving its petrified people even though Reboot showed that the continent had been destroyed by a meteor strike.
Elfen Lied: The "lied" in the title is pronounced "leed"note Phonetic spelling for the German word meaning "song", not "layhd"note Phonetic spelling for the English word meaning "a deceptive false statement (past tense)". The fact that Kouta and Lucy's backstory involves the former lying to the latter about his little sister's gender—which ends up being important to the plot—doesn't exactly help matters.
Pronouncing the word "Eureka" in Eureka Seven as anything but ee-oou-reck-ah will cause certain fans to cringe. Even when you're talking about Eureka, an entirely different series. Doubly facepalm-inducing when you learn that that awkward pronunciation was forced on the localizers by the Japanese (they'd wanted to use the standard English prounciation "yoo-REE-kuh", as in the word meaning "I have found it", or the city in California), and also that the actual proper pronunciation of the word, taken from the original Ancient Greek, is supposed to be something along the lines of "HEOO-ray-kah" (εὕρηκα). Note the "h" at the beginning –- the initial vowel is aspirated. Also, "eu" isn't quite a diphthong; blend the "eh" and "oo" together, but not entirely. (Modern Greek is another story entirely; the word is pronounced (approximately) "EF-ree-kah".)
Spelling the (obviously western) names of the Elric brothers Ed and Al as Edo and Aru — after the Japanese mispronunciation due to a lack of most final-consonant sounds in the Japanese language (in this case -d and -l) — will automatically brand you as a noob among Fullmetal Alchemist fans.
Some people used to insist that there was a character named Edvard Elric in the Fullmetal Alchemist series, who lived in "Amestria" or even "Shamballa". As you can guess, the former shows up infrequently online where text is far more common than speech, but the rest were fairly common amongst almost-but-certainly-not fans at one time.
Also, you probably shouldn't call Al a robot… (a) because he's not; he's a soul bound to a suit of armor; and (b) because several fandom members will get mad at you.
Inuyasha: The name of Inuyasha's sword is the Tessaiga — 鉄砕牙 (てっさいが), not "Tetsusaiga" — てつさいが. It's spelled with a sokuon — small つ (tsu) character, which denotes the gemination of the initial consonant of the symbol that follows it. note The English subtitles use the incorrect latter spelling and Richard Ian Cox pronounces it "Tett-sai-ga", which admittedly is closer to the correct pronunciation than the subs are.
JoJo's Bizarre Adventure: As many of the Stands and characters are named after real-life bands, songs, and musicians, many dubs, subtitles, and other releases change the names to more legally acceptable alternatives. The fanbase is generally not fond of this — call Kira Yoshikage's Stand "Deadly Queen" at your own risk.
Little Witch Academia (2017): Andrew is not Akko's Love Interest. While the two were originally planned to be lovers at one point, this has since been scrapped and the two are strictly friends in the final product (despite some minor Ship Tease), with series creator Yoh Yoshinari describing them as having a "sort of playful guy-guy relationship" in one interview. Saying that Andrew is canonically Akko's lover is a sure fire way to get you corrected and/or mocked by more knowledgeable fans.
The girls are not preteens; they're teenagers in high school. Calling them ten or eleven years old will not sit well with some fans. It's at least somewhat forgivable for someone who isn't a fannote The art style makes the girls much shorter and younger-looking than the majority of adults, but more importantly their sailor uniforms are out of place; those are far more common in middle schools. You can thankSailor Moon for the confusion, but anyone who has watched even one episode should know better.
And it's Lucky Star, not Lucky Stars. And no, it does not refer to anything or anyone in-universe, so don't make the mistake of calling the girls Lucky Stars.
Try calling it "nay-roo-toh" or "nuh-roo-doh" instead of "nah-roo-toh".
Same goes for stressing the second syllable, calling him "nah-ROO-toh," as if the name is Italian or Spanish. Though people do pronounce it that way in Italy.
Don't even think about calling Haku a girl. Same applies for Deidara.
The team of Naruto, Sakura, and Sasuke is Team 7, period. Do not refer to them as "Team 1". Also, do not refer to the team of Neji, Tenten, and Rock Lee as "Team 9". They're Team Guy.
On at least one forum, posters can be targeted by cries of "NEGIMA BANNED!!" for calling Negi's mother Akira (her name is Arika) or referring to his cousin Nekane as his biological sister. Generally, though, Negima fans seem fairly understanding, because there'sa lotto keep track of…
Never ever refer to Monkey D. Luffy as simply "Monkey". This one is particularly bothersome to the fanbase due to mockery of the series early in its lifespan.
There are three English dubs of the series. There's the infamous Bowdlerised4Kids dub, the popular, much more well-received, uncut Funimation dub, and the more obscure short-lived Singapore dub that aired in Asia... DO NOT MIX THEM UP!
Implying that 4Kids still has One Piece is a major berserk button to supporters of the Funimation release. Admittedly, this has become less and less of an issue as time passes, but it was not uncommon to hear such grumblings from casual fans (or purists who only followed the fansub/scans§ they should have known better but either didn't care or found it in their interests to misinform) as recently as 2010 — 4Kids lost the rights to the show in Spring 2007.† They also de facto ceased to exist in September 2012, declaring bankruptcy and selling off their remaining anime assets to Saban and Konami, but that's a story for a different wiki page.
Oshi no Ko: Do not say that Ryosuke Kaihara, the crazed fan that killed Ai Hoshino, was Ai Hoshino's ex-boyfriend, that Ai's ex was a serial killer, or confuse the two characters with one another. People can mistake the two characters as one in the same as Ai's ex, Hikaru Kamiki, did collaborate with Ryosuke in the murder and is who Aqua wants to exact revenge against, but he was not the one who carried the murder itself out.
The two girls in Please Twins! are not the twins, and assuming they are may be hazardous to your health. It's actually about two girls who each believe themselves to be the sister of the male lead, and wind up in a Three's Company sort of sitch until they figure out which is which. The twin is Karen. Or Miina. Depends on whether you're talking about the show/manga or the light novels, respectively.
Project A-Ko: The main character is pronounced "aye-koh" not "ah-koh".
Occasionally someone will refer to Puella Magi Madoka Magica as "Magical Madoka," or something along those lines. This doesn't go over well (especially if you pronounce it muh-DOH-kah instead of MAH-doh-kah). "Madoka Magica" and "PMMM" are the preferred abbreviations.
For a Ranma ½ fan, the use of "Nermia" is akin to a boot to the head. For those who don't understand, the correct name (which is an actual district in real-life Tokyo) is "Nerima".
Revolutionary Girl Utena: Referring to Anthy Himemiya as "Anshii" has been known to instill homicidal rages in fans of the show, due to "Anshii" being nothing more than a Japanese pronunciation of the actual Greek name (seeing as Japanese does not have a "th" sound so has to approximate it with a "shii").
Soul Eater: Do not refer to Crona as explicitly male or female, as the character has an Ambiguous Gender (and in fact might be neither, non-binary, or both for that matter).
Many people who got into the series by the anime think Chiba's full name is "Chiba Saorin". "Saorin" is actually a nickname used by Sasa, her name is "Saori". "-rin" is often added to a female friend's name in Japan. Fans will make you notice if you call her that.
Don't call Nitori a boy or Takatsuki a girl. Don't say they're Wholesome Crossdressers and not transgender. The fans hate that, even though Takatsuki's gender actually turns out to be up in the air.
. Saying that Andrew is canonically Akko's lover is a sure fire way to get you corrected and/or mocked by more knowledgeable fans.