A lot of things annoy me, i'll admit it.
But what annoys me most is when people don't have their fudging facts right in Fanfiction. I, and a lot of others, check my facts if i'm not share. I don't just put something down! If i'm going to ignore something I warn my readers or put my story in a time setting BEFORE whatever the event/issue is.
Examples:
1 ) Fuji Syuusuke is not unbeaten. Shiraishi, being as awesome as he is, beat him. This is one of the things i notice a lot.
2) Alois is a evil/sick little person. It's okay to write characters OOC but its not okay to ignore the whole personally in general.
3) People died. Again: It's oka