We used to work with an annoying Napoleon-like character (read as "short man's syndrome"). We were friendly with him, but tolerated him more than anything else (he was a Director).
One time we put a few large textbooks under the legs of his desk and lowered his chair all the way down. Then we'd left a 7oz beer can on his desk with a straw in it. He'd come in and sit down and look like a 4 year old.
Another time we stole one of the rolling castors from his chair - that was amusing.
I've even taken people's corporate pictures off the company intranet and put them on dating websites in other parts of the country. Then I send the link to a few co-workers and we have a good laugh about it. Who could've known that one of our VP's wanted to hang with 18 year olds in the Dallas area and have a funky baby oil adventure?!
And then there's the time my friend from work (a woman in her 50's) left her license at work by mistake. She called to make sure we'd hang onto it for her. I scanned it and photoshopped it to make her 65 (changed the address too). Then I took it to a bakery that can put the image on a sheet cake. The next day I threw her a phony retirement party in my department. She's such a good sport.
Everybody kept saying, "I didn't know you were that old!" To which she replied, "I'm not! That a$$hole made me 65!"
I crack myself up.