Do unto him before he can do unto you, if you like.
A guy looks at you nastily across a rugby scrum; next maul, you tear his ear off, before he does the same, or worse, to you. You have completed pretaliation. Anything he does after that is retaliation, which referees always come down on harder than on the original malefactor.
"Yeah, he'll be counting his ribs for a month! What a kick! Bet Tonto keeps out of his way for the rest of the game, though!"