Fill someone's hair-dryer with baby powder.
 770
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.
 784
0  

Paint a bar of soap completely with clear nail polish so it won't suds up.
 768
1  

Install the Blue Screen of Death screen-saver on someone's computer.
 846
3  

Write a message on an upside-down paper cup that alludes to something horrible being trapped under it. Leave it on a coworker's desk or in a conference room.
 1499
1