A lot of things annoy you, don't they? :)
When I end up playing everybody in the top 10 in a tournament. (I am almost always somewhere under 20th)
Sometimes when I get a large win streak against someone rated a few hundred points below me I'll decide that it's time to leave after this one last game; and then I lose and I can't leave because then it'll look like I left just because I lost.
Winning a game where I've made 4 blunders and my opponent made 5.