Reverse Door Knob

Remove someone's doorknob and reinstall it with the lock on the inside. Works best if the victim is in the room and the door is locked and you have his/her keys.

Salty Toothpaste

Sprinkle some salt on your victim's toothbrush. When this person goes to brush their teeth, he or she will get a salty tasted treat.

Cream Cheese Deodorant

Scrape off about an inch or so of your victim's deodorant and replace it with cream cheese. It will take a few minutes to sculpt the cheese in place to look like the deodorant. When finished, put the lid back on and back where you found the deodorant. When your victim needs to freshen up again, he will get a cream cheese surprise