I only read the last page of this thread, so if they've already been mentioned, I apologize, but fuck it. Even if they have, they deserve to be mentioned twice.
Nickleback.
I don't think there's a single band on the entire planet that I dislike more then Nickleback. Honestly, I don't even really know what it is about them that ticks me off so much. The extremely generic music/horrible lyrics obviously, but I don't know what it is that makes me hate them more then all the other genericness out there.