Dealing with Trouble Makers
First its fair to say that each forum will have its own limits and levels of tolerance's.
So what may be right for one site may be over the top for another site.
As a guide to a moderate pain in the ass.
1. private message them and warn about a possible ban.
2. ban them if step one fails.
Honestly there really not worth the hassle.
Or if you feel that a Ban is a step too far then thats fine if it works for you. Only you will know the levels at what to act.
Most of all, don't let these idiots get to you.