LMAO that is awesome. Office pranks can be so fun.
We totally pranked one coworker on his birthday last year. Confetti in the fan, taped drawers, plastic tape on ethernet cable (this is always funny in IT) all little stuff like that.
We wanted to fill the top cabinet (door that slides up) with ping pong balls, but had no idea where to find those in bulk, like 10+ alternator size.