How do you take care of trolls on WikiAnswers?

We pluck them bald, dip them in tar and feather them.

Actually, if you find someone causing trouble you can report them to a supervisor. The supervisor will probably issue a warning for a first offense unless it is really obvious the person is just trying to do as much damage as possible. A third offense after two warnings usually results in the offender being blocked. How long they remain blocked depends on just how badly they were behaving.