Irritating: Fr'ex, finishing up a long "bye, good luck with your studies" in an AIM conversation exactly one quarter of a second after the person you're talking to logs off to study. (Sorry about that one, Blaze...)
Disgusting: Gastrointestinal distress known as "the trots", leading to the discovery that parts of your lunch have passed through your digestive system entirely unchanged.
Anyway, back to continuing on homework of my own...