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.
 790
1  

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.
 1549
1  

Paint a bar of soap completely with clear nail polish so it won't suds up.
 803
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.
 810
0  

Put tape over the optical sensor of someone's mouse.
 911
1