Sniper him far away from a high building.
The bullet will be a strong frozen ice ball...i saw it in a movie.
The ice ball will kill him like a bullet, and then melt, leaving no evidence of the bullet and the sniper you fired him with.
Nobody will know who did it, but you'll be a hero to mankind...
If i met him I can honestly say that i'd punch him. until my knuckles were disjointed.
Then when people say 'yo dude what happened?' I'd be all like this guy over here has been assaulting me since january 2010