Arthur: The title character will forever be remembered for the iconic scene of him punching D.W. in Arthur's Big Hit. On the other hand, some viewers haven't lived down how Arthur's Mom and Dad never punished D.W. for provoking Arthur into hitting her in the first place although they didn't know she provoked him.
As their entry on Western Animation Scrappy page would describe, David and Jane Read will probably be forever associated with all the episodes where D.W. acted like a brat and yet they didn't punish her.
Haru showed up in season 3 with an ultra-sexy mustache, and the fandom still hadn't stopped making jokes concerning it. This is partially because a certain Internet parody series played him as a self-absorbed Camp Gay pretty boy several weeks before he reappeared.
Sokka and Momo accidentally get strung out on peyote for a day and a night in the desert. Inevitably, Sokka was afterwards forever depicted by fans as the go-to character for any Mushroom Sambas. Probably because as soon as he recovered, he licked something off a cave wall.
Katara: You've been hallucinating on cactus juice all day, and then you just lick something you find stuck to the wall of a cave?! Sokka: I have a natural curiosity.
Aang's kiss screw-up in "The Ember Island Players". He kisses Katara once, she doesn't want it, and instantly a certain subset of fandom has decided he's an entitled "Nice Guy" who doesn't care about Katara as anything more than a prize and doesn't deserve to be the hero or have any girlfriend.
In the Sequel SeriesThe Legend of Korra, Mako will forever be the guy who heartlessly strung Asami along, and then made out with Korra without bothering to break up with her (there actually was a breakup scene, but it was quick and done without dialogue, so that's how it looked). It's helped by his portrayal in season 2, as a big part of the problem was the show not properly acknowledging what a huge jerk he was to Asami, so when he does the same thing again, he ends up humbled and admitting he was wrong. And then in season 4 he's well and truly called out on it by Prince Wu (of all people) and his own family. When the Grand Finale ended with Korra and Asami getting a Relationship Upgrade with each other, many fans — and, In-Universe as of Turf Wars, his own brother — can't resist jokes at his expense, even though it's clear that he's moved on and now only views his ex-girlfriends platonically.
After The Reveal that she's bisexual, this has rapidly begun to overshadow every other aspect of her character and even the entire series, despite only occurring in the final episode and not being made explicit except through Word of God. Even on This Very Wiki, you can easily find entries where someone has tried to shoehorn in a mention that she and Asami totally hooked up, regardless of whether or not it's relevant to the trope at hand.
Suyin scarred Lin's face when Lin broke up a robbery Suyin took part in, which their mother Toph covered up before sending Suyin away to live with her grandparents. It was an accident that she immediately regretted (and in fact is the only aspect of her quite checkered past that she's explicitly shown regret for), but Lin is such a popular character that for many fans, this was enough to label her a lifelong criminal who Lin never should have forgiven. Of course, other fans take the opposite route and feel that the episode went out of it's way to vilify Lin so people would sympathize more with Su, which backfired and caused at least half the fan base to dislike Su and dismiss her as a Karma HoudiniCreator's Pet.
It even gets into the real world, as many, many fans are never going to forgive Nickelodeon for its unbelievably poor treatment of what should by all rights have been its flagship show, followed by a pitiful attempt at damage control by putting the final episodes back on TV after the fact.
Pinky and the Brain: Despite the common belief that Pinky causes most of Brain's plans to fail, this is rather overblown. While both Pinky and Brain have caused plans to fail, Pinky admittedly more so, the majority of the time it is usually something that was more or less unrelated to the scheme that caused their failures, or else it was a plan that never got off the ground in the first place. Pinky was often quite helpful, either by doing the leg work, pointing out holes with the plan, or using his superior people skills. There where plenty of instances where they would have succeeded if Brain had listened to Pinky.
Pinky, Elmyra & the Brain: The followup to the previous entry, the entire show was this before it had even premiered, being an effort by the execs at Warner Brothers to turn Pinky and the Brain into a family sitcom-esque romp that forced Tiny Toons regular Elmyra into a central role. The very idea of this was panned by nearly everyone who worked on it, and in turn fans quickly came to regard Elmyra as an insufferable brat who stole the spotlight away from the original duo, essentially serving as nothing more than a third wheel. Elmyra quickly became one of the studio's most unpopular characters of the time, and the show itself was unceremoniously canceled before the end of its sole season. It also ended Steven Spielberg's longtime collaboration with Warner Brothers' animation arm.
The Optimus Prime deaths. Each incarnation does die once or twice, and that's once or twice more than most characters who aren't from superhero comics, but you can't say "he's died a million times" unless you treat all Optimuses (Optimi?) as if they were the same guy.
Ultra Magnus is only remembered by fans for the infamous movie line, "I can't deal with that, now". Not only has it become an internet meme, but it also forever painted Magnus in fans' minds as an arrogant and lazy commander who would rather pass off responsibilities to his subordinates than actually get his own hands dirty. The fact that he's seen coordinating strategies more often than he is executing them doesn't help matters much, but he is more proactive than this misconception paints him as being. On top of that, the original line was said as he was in the middle of trying to pilot a ship that was crashing, so it was less "Who cares?" and more "Kinda busy here!"
Also, from the Transformers Movie, Ultra Magnus "usurps" leadership of the Autobots to the point of insisting the Matrix be merged with his spark, despite Optimus Prime flat out naming Magnus as his successor, and insists that Magnus take the Matrix - Magnus, for his part, even says he's not worthy of it. "Evidence" of this is shown by the fact that the Matrix only glows in the hands of Hotrod, but because Ultra Magnus is the de facto leader at the moment, everyone just ignores it.
That's not quite how it goes, if you watch the full movie; Optimus Prime, in his deathbed, flat out names Magnus as his successor, and insists that Magnus take the Matrix - Magnus, for his part, even says he's not worthy of it.
Remember how G1 Red Alert was always panicky and ultra-paranoid? If so, that makes one of us: In the aptly-named episode "Auto Berserk", when a missile hits him in the face, resulting in brain damage that would have killed him eventually, he starts acting in this manner, to the point of helping Starscream get his hands on a superweapon just to keep the Autobots, whom he believes have turned against him, away. He's fixed later. Fans seem to forget both that he was this way for one episode only due to damage, and quite how dangerous the paranoid schizophrenic Red Alert really was. Even his toy bios go on about his paranoia, as if something we've never witnessed in any episode or comic but the brain-damage situation was in fact his defining trait.
A mild case of Older Than They Think: Toy bios were written (and often toys released) in advance of the characters turning up in related fiction and sometimes bore little resemblance to how the characters were portrayed in the cartoon or comic (Ratchet is described as a party animal, for example). Red Alert's paranoia was used for his Day in the Limelight episode but treated as a temporary state of affairs and ignored elsewhere.
Mix-Mix-Mixmaster's Verbal Tic of re-re-repeating the beginning of a sentence... some-some-something he only actually did in one ep-ep-episode ("City of Steel"). Thank-thank-thankfully. Shrapnel, however, really did repeat the last word of every sentence almost every time he appeared, appeared.
Beast Wars once had a damaged Waspinator think he was Shrapnel... only to start talking like Mixmaster did in "City of Steel".
Sentinel Prime may be going this way due to Transformers Animated, due to his smug attitude, general disrespect for others, and sometimes morally reprehensible techniques. In later continuities, there are some aspects of it, one of the names Zeta Prime has, suggested by the writer of Exodus is Sentinel Zeta Prime, and demonstrates much of the same behavior. The Sentinel in Dark of the Moon seems to avert this. But then it turns out he's worse than the Animated Sentinel, using both sides of the conflict and murdering Ironhide.
Hot Rod/Rodimus Prime probably would have been the Replacement Scrappy in any case, given how beloved Optimus was, but he really didn't help his case by being partially responsible for Optimus' death, distracting him at a critical moment, with fans insisting he did it deliberately. But with how it went down, with Optimus failing to finish off Megatron when he has a clear shot and thus giving him the opportunity to grab a hidden gun, while Hot Rod could have done a better job of helping, if he hadn't intervened Optimus would have died anyway.
In the same movie, there was Soundwave not lifting a finger when Megatron was Thrown Out the Airlock by Starscream, and even veering for the role of leader of the Decepticons straight afterwards, which left something of a tint on his Undying Loyalty persona (which ironically was in full display just beforehand when he carried Megatron into Astrotrain in the first place). This has led to fan interpretations of Soundwave being as ambitious and opportunistic as Starscream (if far more shrewd about it) and only playing a loyal follower until the perfect time comes to usurp his leader.
Transformers even provides a meta-example: Transformers Animated came to a rather sudden end for various reasons. According to some fans, this means that Hasbro loves canceling things and produces shows, comics, and toys for the sole purpose of abruptly canceling them all. Any series people like is met with comments of "wonder if it'll get to episode/issue 10 before Hasbro pulls the plug on it?" and occasionally people ask whether a toy has been canceled after it's already out.
An in-Universe example occurs in Animated with Bulkhead continually bringing up the fact that Professor Sumdac was, well, deceived into rebuilding Megatron.
Tygra in Thunder Cats is known as a weak-willed junkie, despite being addicted twice, only one of which was actually presented as a drug.
Aquaman is commonly haunted by his portrayal in the Superfriends cartoons; as a guy whose only real powers are swimming and talking to fish he was (almost) always useless, to the point of Memetic Mutation. This has actually worked out for him a little, as lateriterations of the character usually go to great (and awesome) lengths to subvert this image.
Unfortunately for Aquaman, this image of him continues to perpetuate via parodies of him in other works, most notably Mermaidman and Barnacle Boy in Spongebob Squarepants.
Wendy broke up with Stan exactly once, in the seventh season of South Park. They got back together in the eleventh season finale and have been together ever since. Yet fanfic writers tend to portray Wendy as a manipulative shrew who breaks Stan's heart again and again. This is usually done to justify Stan leaving her for Kyle. But even some writers who like Wendy latch onto the idea that she and Stan break up and make up all the time.
It may have more to do with the fact how shallow their relationship is shown at times. Both have shown heavy attractions to other characters in an extremely unsubtle manner (Stan once constantly attempted to make passes to a substitute teacher and even gloated about supposedly making love to her to Wendy's face while Wendy became disinterested in Stan in favor of another popular jock less than one season after they got back together). Their less than affectionate relationship was even Lampshaded in Raisins.
In Teenage Mutant Ninja Turtles fandom, April O'Neil's yellow jumpsuit. Honestly, every conversation about the old show dissolves into one about her hotness and jumpsuit, this has even made it into other adaptations, as a reference or actually happening (Hell, in the Back to the Sewers season of the 03 show, she wears one!).
The Fairly Oddparents: The episode "Home Wrecker" had Tootie admitting, through Suspiciously Specific Denial, that she tapped Timmy's phones. "Just the Two of Us!" had Trixie going insane and attempting to kill Timmy when the two were the last humans on Earth (dishonorable mention: "Class Clown" where she throws Timmy under the bus after he saved her from a man-eating plant). The detractors of both have not forgotten these incidents. And let's not forget, although in this case it's an example of the producers never living it down, the horrendous Wonderful LifeSubversion episode, "It's A Wishful Life". It is still heavily criticized as one of the lowest points in the series.
On Codename: Kids Next Door, Lizzie used a "Boyfriend Helmet" on Numbuh 1, and ordered him to destroy his teammates. In several future appearances, she was developed more, given her relationship more depth...but people's minds were already set. She became the single biggest target of Die for Our Ship in the fandom. Admittedly, she remained clingy, but nowhere close to that level.
Total Drama Island: Ezekiel made one sexist comment during his short time on the island. Two seasons later, even though others have shown far more sexist tendencies, Zeke was pretty much labelled a Straw Misogynist, and is still hounded for it.
Gwen- both in-universe and out- will never live down being kissed by another girl's boyfriend. That one scene led to Gwen getting voted out and all her allies abandoning her, (Sierra even referring to her as the 'New Heather) even though she'd been a good friend and strong competitor up till then. In All-Stars, she is placed on the villain team entirely because of this, and becomes their Token Good Teammate.
Starfire of Teen Titans was shown drinking mustard once. It's common for it to be referenced in fan works. She is, however, shown at several points later with a bottle of mustard with a straw in it in the background, even if she's not actually in the process of drinking it.
Spider-Man: The Animated Series - whole show, for the censorship issue. Yes, they couldn't say "die" or "kill," have Morbius suck blood, or have Spidey full-on punch anyone. But it seems that's all anyone says about it lately. In fact, it was an ambitious arc-based series with a lot of depth, emotion, surprises, and the portrayal of Venom that has impacted every adaptation since. Interviews with showrunner John Semper reveal that as it was on FOX - yeah, thatFox - it was a 24/7 battle to keep it that way. And just because they couldn't say "die" doesn't mean no one ever did die.
Professor Farnsworth from Futurama, having been declared dead as a tax dodge some years before, found himself irritated that his son Cubert used this fact to perform a hostile takeover of Galaxy Express.
Farnsworth: You take ONE nap in a ditch and people start declaring you this and that!
And of course, Leela's infamous one night stand with Zapp Brannigan is mentioned every time Zapp makes an appearance in the show. Usually by Bender or, more commonly, by Zapp himself.
After Fry accidentally slept with his grandmother and became his own grandpa in "Roswell That Ends Well", Prof. Farnsworth seems determined to bring it up whenever he can. In "The Late Phillip J. Fry", Farnsworth mentions that his time machine can only go forward, "That way you can't accidentally change history or do something disgusting like sleep with your own grandmother", and in "All the Presidents' Heads" Farnsworth tells Fry "You really screwed the granny this time!" after the latter accidentally alters history.
Sym-Bionic Titan: Xeexi got his Memetic Molester status by mind raping two characters in an episode. Only one instance is really ever noted, but now Xeexi is only remembered as a rapist, even though he's also a tactical genius, and well... dead.
Scott was always a nice guy to everyone unless they deserved otherwise. However, he and Avalanche had a known rivalry due to leading opposing teams, usually Avalanche instigated it, and mostly Scott was defending someone else or simply reacting. However, during season 2, Avalanche had changed. Not as in he developed, but his personality had completely taken a U-turn as he was suddenly in love with Kitty and willing to join the X-Men simply to be close. Obviously, Scott remembers how he's acted and doesn't trust him. When Avalanche proves he's not interested in learning at the institute Scott retaliates by reactivating the Danger Room control for a second to make him trip up, a complete Out-of-Character Moment (he made a joke, completely forgetting whothis is). And when someone starts stealing the X-Vehicles, Scott, as well as EVERYONE thought it was Avalanche. When its all over, Scott apologized for this and offered to start again. Lance decides to quit because, after his time here, he's realized its too much work and not really him. However, the Brotherhood fans and a few others refuse to think of Scott as anything but a petty jerk who, without reason, just hates Avalanche who is nothing but a saintly loving Boyfriend to Kitty (despite that by the end of this season he returns to previous characterization and breaks up with Kitty), and that Scott was the reason he quit, having driven him away with his bullying and accusations when Avalanche would have made a great addition to the team. Sigh. That's two characters remembered for a personality they didn't have, because of one episode and one Out-of-Character Moment.
Similarly, the New Recruits are only remembered by some fans as idiots who only want to cause trouble and if left alone would destroy the world. They only did two stupid things, steal the X-Vehicles, and break into the Danger Room unsupervised. Not only did they learn their lesson, they actually showed they were smarter than previously thought (how many of you could fly a jet or survive a Danger Room session designed for the more experienced children?), in fact, it wouldn't have been a problem had Avalanche and Kitty not got in the way and caused the systems to get fried and fired at two Air force jets. But because one caused Avalanche to quit and another was 'confirmation' people always think of them as Too Dumb to Live assholes.
Many characters in The Simpsons are constantly lampshaded by the things they did in the past (especially the secondary characters). Some character only become known by the things that happened to them.
Meanwhile, more prominent characters in the series have past status quo changes lampshaded around them. For instance, there is Apu, who is now currently defined by his marriage to Manjula, his eight children, and his affair.
Thanks to an unexpectedly widespread Memetic Mutation, many people will remember Groundskeeper Willie solely for calling a group of French students at Springfield Elementary "ya Cheese-Eating Surrender Monkeys!" It's the one thing he has ever said about French people, derogatory or otherwise, and longtime fans of the show will tell you that Willie has contempt for people of many different nationalities, including his own. ("Damned Scots! They ruined Scotland!")
As for Lisa, occasional references have been made towards her vegetarianism and Buddhism, both of which were made permanent into order to get celebrities Paul & Linda McCartney (3F03) and Richard Gere (DABF02) to make their one-episode appearances in the respective episodes.
Lisa is also well-known for her profile quote "Embrace nothingness!" from the arcade game despite her saying this only once in the actual show.
Then there's Seymour Skinner, who has been referenced by his false identity, as well as his relationship and break-up with Edna Krabappel.
The town of Springfield as a whole will probably be never forgiven for driving Bart to kill himself in "The Boys of Bummer".
In-universe example: In a Robot Chicken skit on G.I. Joe, a new recruit is given the name Fumbles after slipping on his spilled soda. This leads him to defect to COBRA for the sake of revenge. Unfortunately for the Joes, "Fumbles" happens to be a Badass BookwormCold Sniper who is capable of single-handedly killing them all. Even better, at the end of the sketch, Cobra Commander is so impressed that he wants to give the sniper a much better nickname, only for him to coldly respond "It's Fumbles. It's always been Fumbles."
Most of the classic cartoons from the 1930s until the 1950s have a reputation for being nothing more than violent slapstick with a lot of explosions and people hitting each other. Despite the fact that the Bugs Bunny and Daffy Duck cartoons, for instance, are very dialogue driven and a lot of comedy also comes out of the dialogues between the characters.
For that matter, the Censored Eleven are disproportionately referenced in media, even though they comprise less than 1% of all Bugs Bunny cartoons.
Superboy in Young Justice has yet to lose his Emo Teen label, despite the fact that he grew out of it after the first ten episodes and lost it completely in Season 2.
Well, he was still a little emo in season 2, albeit for different reasons since the subplot of Superman refusing to accept him got swept under the rug his angst was re-directed towards a very ugly breakup with Ms. Martian.
Superman being a stubborn, insensitive Jerkass towards Superboy throughout the first season, even though season 2 depicts them as having buried the hatchet on the matter.
No matter what Brian from Family Guy does that might redeem himself, certain fans will never forgive him for vocally espousing his ultra-liberal viewpoints, particularly in the episode "Not All Dogs Go to Heaven."
In Ed, Edd n Eddy, despite showing some Character Development, albeit smug and a follower, Jimmy will always be known for framing the Eds in the episode "If It Smells Like An Ed." Granted, he did frame all three Eds when it was only Eddy who humiliated him while the other two Eds did absolutely nothing to deserve such retribution.
There's also Kevin's actions in the episode "Your Ed Here". Normally only beating up the Eds if they truly deserved it, and has been kind (or at least passive neutral) to them in the past, this episode had Kevin find out Eddy's Embarrassing Middle Name and proceed to go out of his way to humiliate Eddy in order to keep it secret. After Eddy goes through a Humiliation Conga to keep it secret, Kevin proceeds to tell everyone anyways. Needless to say, fans were nothappy about this, and though Kevin quickly reverted to his original characterization (for a while, anyways) the Fandomstill portrays him as a raging Jerkass with no redeeming qualities whatsoever.
Similar to the Mixmaster example above, Roadblock from G.I. Joe is known (and frequently mocked) for his Rhymes on a Dime dialogue; while he did talk like that, he didn't do it all the time. However, most parodies of the character make him say every sentence in rhyme, as if he always did.
One season 2 episode of Superjail! depicted the Twins as cannibalistic, insect-like, and also consuming bleach and other toxins. Even though some of the alien traits depicted in it were not referred to again in the following season, the episode definitely left a mark on fans' minds and fanart and comments will mention them in some way. For some, the episode seemed to ruin the characters and exaggerate the alien nature a little too much. And then you have the fans who claim the characters should never have any fans that like them over the actions they pulled in the episode.
Alice, er, "assisting" the Mistress in the season 3 premiere goes down this way for other fans. Never mind whatever else Alice did before or after that episode, there are some that give her the reputation of "Ruined Warden/Mistress foreverand is in the way".
Hey Arnold! an in-universe example, one episode had Rhonda throw a party in which some characters were not invited for being Geeks. They bring up the literal definition of the word, which repeatedly prompts this exchange: "...And none of us bite the heads off chickens! Except Curly." "Yeah! And that was only the one time!"
Another in-universe example (and deconstruction) occurs in "Phoebe's Little Problem". Phoebe, while accepting an award on stage at a school assembly, accidentally farts into a microphone. The rest of the students won't let her live it down, eventually causing her to become a shut-in. Some of the other students (and Mr. Simmons, the teacher) feel bad for her and try to cheer her up, but their attempts end up making her feel worse. Finally, at another assembly, Phoebe gets on stage and goes on a tirade about how, in spite of everything else she's done, all the other students are reducing her to just being "the girl who farted", as if that was the extent of her accomplishments.
Iggy forcing Arnold to wear bunny pajamas in public in "Arnold Betrays Iggy". Even though he realized his mistake after hearing Sid and Stinky admit to pulling the secret out of Arnold's mouth, Arnold never forgave him, nor did the fans. Even Craig Bartlett himself was ashamed of the episode, and Iggy never made another major appearance again. Sid and Stinky can qualify too, since they were the ones that randomly guessed Arnold's secret about Iggy, and also that they broke the promise they made with Arnold not to give away Iggy's secret. Unlike Iggy, this didn't get the two of them removed from the series.
Itchy And Scratchy were in fact stated by Word of God to be based more on the far more violent Herman and Katnip shorts, yet another Follow the Leader to Tom And Jerry that helped Flanderize the one sided sadism of the cat and mouse dynamic.
To a lesser degree, nearly all slapstick animation associated with the Karmic Trickster formula (especially in the Golden Age era) is believed to be revolved around a tall order Disproportionate Retribution method, with the protagonist being a self righteous little masochist who heckles, brutalises and just acts ten times crueller than the "villain" throughout the entire cartoon over a very minor slight at the beginning of the story. This is despite the fact that many series (the better written ones at least) actively tried to ensure their heroes look provoked. Warner Bros in particular were rather wary of Bugs Bunny turning from a mischievous trickster into a bully, going through an endless number of increasingly malicious antagonists that could look repugnant enough against him, and even having Bugs lose odd shorts he acted up to completely debunk the Double Standard.
Dana Tan, Terry's girlfriend in Batman Beyond, is best known for constantly breaking up with Terry and is also often called a Damsel in Distress who's constantly getting rescued by Terry/Batman. In fact, while she's often mad at Terry, she only broke up with him once; except for that one episode, they're always still a couple, not in an on-and-off relationship. On the Damsel in Distress front, she only has to get rescued in one episode and is briefly in danger in the movie, and neither time does she passively wait for rescue.
In-story, Terry is constantly reminded of his delinquent record, despite having spent months in juvenile hall.
Onion is seen as evil by a lot of fans because one episode showed he steals tickets from arcade machines and another had him wreaking havoc with Pearl's replicator that Steven traded him for a toy that it turned out he stole from Steven in the first place.
Tumblr was quick to latch on to a brief scene in the episode "Clarence Gets a Girlfriend" where Jeff expresses resentment over not being able to get a girlfriend because he's a nice guy, sounding a lot like "nice guys" who only act nice to girls because they expect to get something out of it.
The legacy of The Flintstones will forever include how they shilled cigarettes in their early days. What makes this tragic is that those TV spots have been censored for as long as almost anyone can remember, so no one under retirement age would know about them if people didn't keep referencing them on YouTube or on trivia clip shows purely for schadenfreude.
Aardvark: I hope none of the other anteaters saw that. Ooh, I'd never live it down!
Thomas the Tank Engine tends to get flak from many fans over odd episodes that display Fantastic Racism towards the diesels (particularly in Misty Island Rescue, a feature length episode which is generally considered poor in every other quality anyway).
While Edward's Character Rerailment is a well appreciated blessing to many fans, the phrase "new fangled nonsense" will forever make them cringe in dispair.
SpongeBob might never live down the fact that he mistreated Gary for "bothering" Puffy Fluffy in "A Pal for Gary", even though it was Puffy Fluffy who tormented Gary.
Patrick tortured Gary in several unfunny ways in "Pet Sitter Pat", stole SpongeBob's Krabby Patty toy in "Yours, Mine, and Mine", glued SpongeBob in a wringer in "Stuck in the Wringer". He also gets a lot of heat for "The Card" over a single joke.
Mrs Puff is known for trying to murder Spongebob in "Demolition Doofus".
Squidward's most infamous moment may be when his toenail was ripped out when he dropped a chair on his foot in "House Fancy". Yeah, he's more of a Butt-Monkey than anything else. When he needs to be an antagonist, he has relatively few low points, but "Little Yellow Book" seems to be the most infamous.
On a meta level, the SpongeBob "fandom" will NEVER be able to forget the way they reacted towards certain post-movie episodes, especially ones on This Very Wiki and Deviantart, mainly due to how childish they were about it, how they stole most of their opinions from Mr. Enter, who in and of himself was exaggerating, the fact that they were talking about them years after they actually aired, and especially the way they treated writers of the show (which even Mr. Enter regrets and has tried to rectify). Although it's started to settle into a more peaceful state, with most of the haters giving up talking about it and the newer episodes being much better, there's still a terrible aftertaste in the SpongeBob community, at least when former haters aren't being ridiculed as a mere passing side comment.
Buttercup of The Powerpuff Girls has been shown to be a decent person even though she is often rude and aggressive, but a Vocal Minority fans outright despise her due to making Bubbles cry by breaking her chalk in "All Chalked Up" and smiling while her sister cried over it, or when she threw glue at Elmer in "Paste Makes Waste", although she did apologize for that (despite being forced to by Blossom and Bubbles).
Mitch Mitchelson, despite being a recurring character, seems to always be remembered solely for torturing the class pet in "Gettin' Twiggy with It".
The cowardly Scooter from Challenge of the GoBots actually does more than just whine about the danger he has to face, manages to save the day all by himself on occasion, and even gradually grows out of his cowardice as the series progresses, but fans will always remember him as a complaining coward who'd rather surrender than put up a fight with the Renegades.
The Loud House has a number of really bad cases of this, especially when they involve one character treating main character Lincoln in a rude or cruel way. Some notable examples:
Luan Loud has trouble living down the almost sociopathic level that she takes her signature jokes/pranks in "April Fools Rules" (to the point that she even scares her parents) and being allowed to get away with it for the most part. The episode "Fool's Paradise" further tarnished her image in which she trapped her family in a motel where she can torment them with mean-spirited pranks for her own sick glee.
Kaeloo: In the episode "Let's Play Courtroom Drama", Kaeloo pulls a cruel trick on Mr. Cat by emotionally manipulating him. After that episode, a lot of fans consider her to be a Manipulative Bitch and feel sorry for Mr. Cat, despite Kaeloo mostly being nice to him in other episodes until he pushes her past Rage Breaking Point, and Mr. Cat himself has done worse things before.