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

 691

3  

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!

 1318

0  

Hide all of the desktop icons on someone's computer and replace the monitor's wallpaper with a screen-shot of their desktop.

 729

0  

Fill someone's hair-dryer with baby powder.

 633

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.

 1256

1