Punch a pillow. Go somewhere where no one will hear you and YELL (be sure no one hears you tho!). Run until you get one of those side stitches and have no more breath and then run some more.
Or.... just walk up to 'em and have at their shins. I have found that shin kicking usually results in an immediate counter reaction of a punch from the receiver of the kick, so be sure to duck... and wear shin guards in case they kick back! (Just kidding).