bang their mom.
Go into a locker room (or anywhere for that matter) and jam a toothpick deep into the locks of all the locked lockers. Sweaty bastards won't be able to change clothes, lol.
That's a shitty thing to do. If you have more time before the mark comes back use toothpaste instead. That shit dries as hard as concrete and you can't use tweezers to get the shit out.