1. Take a mug and fill it with coffee.  Then, cover the top with something like an index card or a picture.  Keeping the index card on tight, and without spilling, flip over the mug on your victims desk.  pull out the index card quickly to avoid spilling.   Your victim will spill the coffee everywhere, and theres nothing they can do.

2.  Take a pen from your victims workspace, it has to be a capped pen, and unscrew the top.  Take out the ink.  Find a matchbox and cut off the strip used to light the matches.  Shove the strip inside the cap, make sure it wraps around the inside.  Shove two matches in where the tip of the pen used to be.  Cap the pen, and when the victim opens it, a fire will light.  (For pussies: you can fill the pen tube with water, which will put the fire out right away)

3.  Find a victim with a door knocker on their front door, and no screen door.  Make sure that there is a place that you can hide across the street. (like a bush or a big tree) Attach a long piece of fishing line to their door knocker, and get in your hiding place.  Pull the string and knock on the door repeatedly.  When the victim comes out, wait for he/she to go back in, and then knock again.  Do this as many times as possible, before they find the string. (If you really want to be an asshole, go out at 2 in the morning)