Office Pranks
Mouse Problems

Making your coworker's mouse malfunction.
Step 1: Put a piece of tape over your coworker's mouse laser or mouse tracking ball.

Result: If your coworker has a laser mouse and you use clear tape, the mouse will likely partially work. It will be hindered just enough to annoy your coworker and it will likely be hidden enough so that they won't know what the heck is going on. They will replace the batteries, re-plug in the cable, and restart their computer multiple times.