Paint a bar of soap completely with clear nail polish so it won't suds up.
Change the coffee in the office coffee maker to decaf.
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.
Install the Blue Screen of Death screen-saver on someone's computer.
Hide an alarm clock in someone's bedroom and set it for 3:00 a.m.
Fill someone's hair-dryer with baby powder.
Pull on a coworker is to press ctrl+print screen on their workstation, then paste it into Paint, save the pic, and set it as the desktop background. Move all of their icons to the trash. When they get back to their desk, clicking won't accomplish anything!
April doesn't fool Chuck Norris, Chuck Norris fools April.
I just recently discovered that there is a national holiday named after Atheism. April FOOLS day. Like this story in the name of Jesus.
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.
Put tape over the optical sensor of someone's mouse.