Want to mess with your work neighbor? Here's a great one. It's called the frozen computer. You're going to open up a bunch of windows in your own computer. Search for rash creams, Russian bride websites, anything that's embarrassing. Then you're going to take a screen shot, save it, put it on your flash drive, pop it into his computer.
Once the flash is put into the computer, you're going to open it up, take your screen shot, move it on to the desktop Then you're going to open system preferences, going to go to desktop and screen savers, put it into your desktop background, close out all the windows, eject your flash drive, and you're done.