Along those lines I like to take a screen shot of someone’s screen. Then, set the screen shot as the back ground issue and make sure to hide the windows bar to autohide. First, they think it’s the mouse battery, then, the keyboard, then panic when they restart the computer and the same thing is going on.
Swapping left and right mouse buttons are pretty fun as is reversing the direction of travel.
Autocorrect pranks are always fun.
Tape auto fresheners under desks.
Spring loaded package peanut traps in file cabinets. This one takes some extra hardware and planning.
ALWAYS lock your computer when you work with nerds.
The BSOD screen saver is always good.
I've always said be nice to the geeks you work with. They are capable of creative and inventive ways of taking revenge.