There is a potential system that would minimize this problem, but I’m not sure how to set the flags.
If someone is found griefing (primarily a PvP suggestion) after a warning or some kind of notice, make him visible on the overhead map as a target. You may be surprised at how many times they will die, just from sport.
I know if I were a designated target in a PvP environment, I might just move servers and learn a lesson.
What confounds me is how to determine if a player repeatedly exhibits this behaviour or if someone is just pissed at him. It may lead to someone being a griefer just by calling someone else a griefer.
Not trying to present a solution, just planting a seed.