I've had users stir things up or break some rules. I've had good luck contacting them and telling them that they are "on probation"... this seems to work better than banning, because banning makes them mad.
I give them a time limit.... on probation for 2 weeks..... etc.
Then I use my Private Moderation hack (in the beta mods forum) to place them into private moderation. Then all their posts have to be approved. I reassure them that they can still participate.... just all their posts must be approved.
If they behave..... moderation will be removed after the time limit. If they continue... the next step is banning.
It's worked on problem users. Doesn't help with outright trolls.... but it's worked well.
