Fill someone's hair-dryer with baby powder.

 723

1  

Take a squirt gun into the rest room stall next to someone and shoot little drops over the wall every couple of seconds while pretending to pee.

 722

0  

Hide an alarm clock in someone's bedroom and set it for 3:00 a.m.

 760

0  

Install the Blue Screen of Death screen-saver on someone's computer.

 779

3  

Place a pair of pants and shoes inside the only toilet stall in a rest room to make it appear someone is using it all day.

 703

1