Ban him, block his IP-address from signing in again and throw all the threads that he has started into one superthread and lock it, so that it can sink to the bottom of this forum and never rise again.
It sounds hard, but I learned my netiquette on that MA site with the bull and unfortunally this is still the best way to get rid of "counterproductive members" (aka trolls). Remember that it's THEIR actions that decides THEIR fate.
$0.02