There are a few things you can do
Since you use vbulletin:
- Let him register again and immediately put him in Tachy Goes to Coventry so that no one can see any post he makes. He will wear himself out eventually.
- Install the Miserable Users hack (since your profile says you use 3.0.x, you should use this version:
http://www.vbulletin.org/forum/showt...threadid=59727)