Erzengel picked this up before me, so i'd leave the last decision to him, however i was there during the whole "duel" business, couldn't see the twing at spawn though cause i was relogging my character. From the looks of it the guy is very rage- prone , so at least some kind of a warning is recommended just to prevent him from doing worse things in the future.
Edit: oh boy, just checked his ban history... Erzengel, good luck =).