I hate people who make sweeping generalizations, specifically ones that discredit entire genres of music/film. (yes, I know that I am making a generalization here, so I am a hypocrite, whatever)
To be more specific:
I hate people who say they hate all anime after watching one shitty seires. (to me that's as stupid as saying "I hate all live-action movies and television" Yes, the majority of anime is shit, just like the majority of tv is shit, but if you dig a little you can find something targeted at you)
I hate people who say they hate all books. (only possible exception for this is people who hate reading because of dyslexia or some such... but they don't get a full pass, because they could still listen to books on tape)
I hate people who say they hate all of music genre X. (If you really listened to every song from a genre you'd find one that you approve of. For example, I dislike most rap, but there is one or two rap songs that I will admit to liking.)
I hate people who say they hate Comics, because they don't like super heroes, when there are countless comics that don't have anything to do with super heroes.
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Some other stuff worth mentioning:
I hate people who start fights in forums or games to get attention.
I hate passive-aggressive behavior.
I hate people who don't use their blinkers while driving.
I hate people who can't take a joke.
I hate guys who wear their pants around their thighs and let their boxers hang out.
I hate stupid guys.
I hate stupid girls.
I hate people who don't like learning.
I hate people who complain about money after charging up a truckload of debt on a credit card.
I hate steamed cauliflower.
I hate people who swear constantly. (Swearing occasionally when extremely angry is okay)
I hate racist people.
I hate black people who use the n-word, but are offended when people of other races use that same word.
I hate nonsensical/overly philosophical endings to otherwise normal series/movies.
I hate console fanboys who believe that they are unbiased.
I hate pregnant women who ignore warnings about drugs that can cause birth defects.
I hate pandas.
I hate people who try to win arguments by busting out overly complicated theories into a casual conversation. (a person once tried to win an argument about social drinking by bringing up the allegory of the cave)
I hate people who drink until they need someone to babysit them.
I hate Twilight's take on Vampires.
I hate people (and especially reviewers) who liked the movie "Coraline" (however, the book, "Coraline" is awesome)