Someone posted this idea on here a while back:

Take one of the welcome mats that scream when you step on them, and put it at the base of someones tree. Cover it with leaves so when they go to get up in their tree, they step up on it and it screams in the pitch black. That sure would scare the HELL out of me.

Or if you wanna piss someone off, go to a shooting range and collect all the .243's laying on the ground. Take them and put them up in your buddys treestands...they go up opening morning and see their stand littered with shells from a .243 and wonder who's been hunting their stand. They'd probably come back to the camp one pissed off hunter.