I've done a number here at work. Many desk drawers and overhead-bins were filled with packing peanuts. One co-worker has his desk sitting facing the door, back of desk is against open air. Fishing line was tied to his phone, and looped around everything on his desk. End of line was brought under the front of the desk and tied to his chair so when he pulled his chair out, everything fell on the floor. Teehee.
Another co-worker who is petrified of snakes has a can with one of those spring-loaded snakes inside it (the gag peanut can) rigged to his drawer so when he opens it, it will spring out.
One I did last year ::snicker::....got a box, about the size of a shoe box, plain brown, ruffed up like it's been thru shipping. Went to reproduction and asked them for their three-hole punch machine cutouts (remembles millions of pieces of confetti). Put into box, cut one end off, put another piece of cardboard over the top so as to flip it over without spilling the confetti. Flip box over and slip cardboard out. Now the box has open side down with all the confetti on the desk, but still contained in the box. Get FexEx airbill and fill out (in someone else's handwriting) so as to entice victim to pick it up. Pick up box, confetti goes all over the place. Wotta riot.
Another favorite; I have a piece of standalone software called Kaboom. It plays random WAV files that you load to play at any interval you choose. It goes off with nothing in the task tray, nothing on the desktop and no obvious way to shut it off. It also controls the volume teehee. Random amusing WAV files play during the day and can't be shut off even by shutting down. ::snicker::
No one gets me....cuz they know I'll get them back. =)