I have several users who for literally years have trolled my forums. Any positive contributions they've made have been matched by attempts to disgust and/or harass, and then my regular members flame them and whine when they fight back. I don't want to add any kind of lame moderation queue or anything like that for a few idiots who refuse to get a life, a clue, or hit by a bus. What are your favorite ways to annoy problem users?
Well, if you're well-liked on your site, just thoroughly mock and ruin everything they try to do. Getting a lot of smart users to fight them back is always fun.