The strong taking advantage of the weak. Drives me crazy. To the point that I often just can't stand it and say or do things I shouldn't. If you're strong, it's your responsibility to look out for the weak.
Hunting for sport. Especially if you don't eat the meat. Killing for fun.
Rap music. Especially Gangsta rap. Yeah, I know. Poetry of the streets. Bleech.
Religious arguments or discussions where parties think their way is the only way.