You can get the name of his computer and ban him from that, BUT, he can always change the name of his computer.(if he's smart enough to work that one out)
If he is being seriously insulting- to the point of remarks that could cause serious offense, then I suggest you track down his isp, and get him in trouble via them, most isp's don't like having trouble makers using their service, especially if the trouble maker is hacking, flaming, spoofing etc.
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Sometimes, when my code just won't behave, I take it outside and make it listen to britney spears music, and when it comes back it's really well behaved. I wonder if it's suffering from post tramatic stress syndrome now..