People who repeat themselves. People who think you're stupid. Kids under 13. Banshee noobs in Halo...grrr
i'll add another: skinny girls who keep complaining they're overweight and then resort to ridiculous diet like half an apple for lunch and a slice of pear for dinner.
Slow drivers, specifically people who never get out of the fast lane regardless of how slow they are moving. HEY! HEY! some of us want to get to our destination...TODAY! It's like I'm almost certain they'd never look in their rear view mirror unless you ram them from behind! MYA people, MYA!!