This guy that has been my acquaintance for about a year smeared syrup on the back of my shirt. I'm pissed and want to get back at him, I need a subtle but devious prank to play on his locker. Note: I do not have his code to access it. What are some nice little "surprises" I can give him? Edit: my lockers are really thin and don't have vents, that's why this is so hard to figure out