Put tape over the optical sensor of someone's mouse.
Hide all of the desktop icons on someone's computer and replace the monitor's wallpaper with a screen-shot of their desktop.
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!
Install the Blue Screen of Death screen-saver on someone's computer.
Fill someone's hair-dryer with baby powder.
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.
Q: What did the elf say was the first step in using a Christmas computer? A: "First, YULE LOGon"!
Paint a bar of soap completely with clear nail polish so it won't suds up.
Q: How many Microsoft engineers does it take to screw in a light bulb? A: None, they just declare darkness the standard!
Chuck Norris can infect a mac with pc viruses.
I just recently discovered that there is a national holiday named after Atheism. April FOOLS day. Like this story in the name of Jesus.