Irrational Hatred

This is when a character hates and/or blames another one for something that is at best only partially their fault. Evidence may be willfully ignored or misinterpreted to support their position, and it usually takes a titanic effort to get the hater to change their mind (if any is even possible).

This trope comes in a few variations that, while distinct enough to probably be their own tropes, will be grouped to avoid confusion. They are: misplaced/overinflated blame, inarticulate dislike and ungrounded jealousy/prejudice.

When it's misplaced or overinflated blame, the hater assigns blame to the character (often more than justifiable) not through some misleading evidence, but out of an emotional need to blame someone (often in situations where no blame could be assigned). If the character did deserve some blame, the hater will react much like in a Rant-Inducing Slight or Minor Injury Overreaction and latch on to them as a convenient target. What's sad about this is that a hero who suffers from Samaritan Syndrome may well let the hater nurse this grudge if they actually did fail, even in some minor way, out of overblown guilt. Some heroes will allow this even if they didn't earn it to allow the hater an outlet, which usually comes back to haunt them.

An inarticulate dislike is (oddly) easier to quantify. The hater has a genuine dislike for the character, but either can't or won't put it to words. It may be that the hater feels insecure or jealous, and rather than face those feelings, they sublimate the dislike into a nebulous cloud of barely coherent Insane Troll Logic directed at the character. Or it may be a truly irrational hatred that has no basis in reality. Because of this vaguness, the hater may end up disliking seemingly random traits of the character, which can be noted when it isn't an issue if other people do it.

Lastly, ungrounded jealousy or prejudice stems from hating something that the character has no control over, such as being disabled or extremely beautiful. While in these cases, the hater has a concrete "reason" and definable focus for their hate, it's just not rational to hate someone for something they have no control over. Now, if said character abused their disability or advantage to manipulate others or rested on their laurels, it wouldn't be this trope.

It bears repeating that in all of these cases, the hater may suffer from You Are What You Hate due to Internalized Categorism, and is sublimating the blame, guilt, or jealousy for some other thing the hated has, is, or has done into a more "acceptable" irrational hatred rather than face the ugly truth inside themselves. Getting the hater to notice this or admit to it usually requires that they Kick the Wrong Dog in the pursuit of their prejudice.

Compare the Inspector Javert, who pursues someone regardless of their culpability. The Armoured Closet Gay's hatred of gays is usually born of this, and so is most hatred for any Category Traitor.

Comic Books

 * Spider-Man "antagonist" J. Jonah Jameson, while almost never an outright villainous force, scratches the limits of the impossible in regards to his hatred of Spider-Man. He despises him with extreme passion, constantly referring to him as a menace, nevermind the fact that Spidey has saved Jonah's life, not to mention New York and even the entire world, on a regular basis. Whether or not there's an explained reason for it depends on the adaptation, but even when there is an excuse, it generally falls apart given everything Spider-Man's done for the world.
 * Eddie Brock wasn't much better. His entire reason for hating Spider-Man was that Spidey unwittingly exposed his shoddy journalism. It took decades in real-time and years in comicbook time for Brock to get over it and become a better person.
 * Lex Luthor's legendary vendetta against Superman has, over the continuities, various causes. All of them agree on the fact that Luthor, in truth has relatively little objective reason to waste so much time, money, and effort on attacking the Man of Steel beyond sheer jealousy. Superman himself has called him out on this numerous times, which only makes Lex hate him even more.
 * Doctor Doom has built his entire career as a supervillain around spiting his old college pal, Reed Richards for a freak lab accident that left him disfigured. Reed didn't actually cause the accident or anything. In fact, he actually tried to warn Doom that his calculations had errors that could lead to disaster before the experiment began. Doom just ignored him out of arrogance. Doom's spent every waking moment since then trying to destroy Reed, his friends, and family because, otherwise, he'd have to admit Reed was simply smarter than him and that he made a mistake.

Fanfic

 * Remus Lupin in the Harry Potter fanfic Family Night has a bad case of Irrational Blame. Basically he decides that it's Harry's fault Sirius died and that he won't come to the titular Family Nights that Hogwarts starts holding (basically four times a year the parents come in to take a look at their children's work) unless Harry improves his work ethic. It soon becomes clear that he has completely unreasonable expectations, insisting even as Harry works himself literally to the point of collapse that he isn't working hard enough. Not helped by the fact that Harry is already blaming himself and therefore thinks that Remus is being perfectly reasonable. Even Snape can see that Remus is being irrational in his treatment of Harry.

Literature

 * Lots of this in the Deryni works:
 * Some members of the Camberian Council feel free to deride Morgan and Duncan for being half-breeds (having one human and one Deryni parent) as if they could choose their parents.
 * In The Bishop's Heir, Caitrin twits Archbishop Loris over the failure of his assassin to kill Duncan McLain; in response, Loris mutters, "The archfiend Morgan came to his aid. He used his Deryni sorcery to heal him." Never mind that healing was a miraculous sign of Christ's divinity.
 * Morgan, Duncan and other characters dissect anti-Deryni prejudice on the part of humans much the same way; people don't choose their innate talents any more more than they choose their physical traits or other skills, so it's better to consider what people do rather than what they are.
 * Harry Potter: Severus Snape has always hated Harry and treated him like dirt throughout the entire series. While the two cultivate a genuinely antagonistic relationship with one another, nearly all of Snape's hatred towards Harry stems from his more legitimate hatred of Harry's father James.
 * Jane Rizzoli of the Rizzoli and Isles series of books is a plain/average looking woman who frequently displays an irrational hatred of beautiful women, as if they had any control over how they looked, and/or somehow stole their good looks away from her.
 * In L. Jagi Lamplighter's Prospero's Daughter, Eramus is always at Miranda. Even learning he was cursed to feel that way does not give him pause.
 * In The Wheel of Time, Gawyn Trakand displays this trope toward the main character, Rand. When second-hand news states Rand has done something terrible to Gawyn, he believes it immediately and develops an all-consuming hatred for the man despite two loved ones who both defend Rand wholeheartedly. This includes misplaced/over-inflated blame as the terrible event is something for which Gawyn feels an emotional need to blame someone as he can't go back and change what happened; later it becomes ungrounded jealousy/prejudice due to Rand being the hero.

Live Action TV

 * In Scrubs, Dr. Cox from Scrubs has an irrational hatred of Hugh Jackman. John C. McGinley, his actor, jokes that he hates him because he's a better actor.
 * Crais from Farscape had an irrational, borderline psychotic hatred of protagonist John Crichton, who accidentally caused the death of Crais's brother. He eventually admitted he was actually trying to protect his rapidly waning career.

Manga and Anime

 * Naruto: This is a big part of Sasuke Uchiha's motives in the later half. While he had a perfectly legitimate reason to hate his elder brother Itachi for the murder of the entire Uchiha clan, he let himself get consumed with Revenge Before Reason. As a direct result, when he later learns that Itachi, his craving for vengeance transfers over from Itachi to the Leaf Village as a whole for
 * Vento of the Front in A Certain Magical Index despises the Science Side of the world because she and her brother were critically injured in a ride that claimed to be scientifically proven safe and doctors were able to save only one of them.
 * A dominating theme in Hayao Miyazaki's Princess Mononoke.
 * In One Piece, the leaders of the New Fish-Man Pirates hate humans for years of Fantastic Racism, but apparently
 * Fisher Tiger, one of Fishman Island's heroic figures, also had an irrational hatred of humanity, though he did have that firsthand experience to a major degree when . He knew intellectually that good humans existed, but could never fully get over his own hatred..
 * In the first El Hazard OAV, Jinnai comes to view Makoto as a hated enemy and rival, for no other reason than he's Always Second Best when compared to him. Makoto in his turn, isn't even aware that his actions have been pissing Jinnai off.
 * In Pokémon, Harley has an irrational hatred for May. It's later revealed that his dislike of her stems from an incident in his childhood, when a girl who looked like May stole his snack in kindergarden.

Real Life

 * Most Racists
 * Pretty much all unless you count the borderline examples(I dislike this cultural trait, I get nervous around because one beat me up once, etc). Actually hating someone because of who their parents are is a silly thing to do as well as unjust and often more harmful to the hater then the hated in any event.
 * Arguably extreme Child Haters hatred towards children.

Video Games

 * The character Grace from Dragon Age 2 exemplifies this trope. If Hawke assisted her in escaping the templars in Act 1, she is eventually re-captured and brought to the Gallows. She blames Hawke for the death of her lover Decimus, an insane blood mage who attacked Hawke without provocation even after Grace begged him not to, as well as her forcing her to go on the run with no supplies and practically no time to prepare, ignoring the fact that she and her fellow mages would have been slaughtered without Hawke's intervention. By Act 3, her grudge has bloomed into a full-blown desire for revenge.

Web Comics

 * Susan from El Goonish Shive is a self-aware case. She knows that her dislike of men is irrational ever since she understood that it was little more than a backhanded excuse for her father being an unfaithful jerk. Despite this, she still can't help but instinctively mistrust mens' intentions.

Western Animation

 * Family Guy: Quagmire's hatred for Brian plays with this. As he once blatantly pointed out, he has perfectly good reasons not to like Brian, however more than a few times he often thinks the worst of him for a minor inadvertent offense, leading him to excessively lash out verbally and physically.
 * Meg herself called them out on how she's always being treated as a Butt Monkey, and very quickly discovered that without her in the family to—in her own words -- "act as a lightning rod", the entire family would completely collapse in on each others own personal problems.
 * Demona from Gargoyles has nursed a murderous hatred of humanity for over 1000 years because humans killed her clan. It's irrational because her clan only died because she betrayed the humans that liked/tolerated her clan to the humans that ended up killing them out of paranoia. This happened twice. In one episode, the Weird Sisters forced Demona to admit that she was far more culpable for the deaths of her kinsmen than humanity. After the trance was over, she angrily backpedaled and went right back to plotting genocide.