If you are a nerd (or just work in an office environment), there are some awesome, mostly easy to accomplish pranks in this list. For example:
10. The Wrath of Rotation
A simple but quick and always amusing prank is putting the screen rotation hotkeys to uses Microsoft never intended. Just run by a co-worker’s desk, reach over and hit Ctrl-Alt-up or down to rotate their monitor orientation. If you have some alone time, you can one-up it by also going into the Control Panel and setting their mouse to left-handed. They’ll spend 10 minutes with their head tilted sideways trying to figure out what the hell is going on.
Find the whole list here: The 25 Best High-Tech Pranks.