Call for submission; How you pranked your professor/PI - (Sep/03/2010 )

I am just looking for a list of awesome pranks (best if science/biology/lab/class related). This is very much appreciated.

e.g.

If you are have a foreign hard-to-pronounce name, correct the professor's pronunciation every time he says your name. Eventually, he'll get it right. But immediately correct him again and fabricate a new pronunciation.

While he was at a conference, I convinced someone to let me into his office. I emptied his coffee tin, cut a hole in the bottom, and swapped out the coffee with candies.

When he returned, he lifted the tin to make a fresh pot of coffee...and commenced swearing in his native language so loudly that everyone in the graduate student workroom heard him! That gave me enough of a heads-up to start running for cover.

Oh, and this one was an accident , but to the same end:

We had just acquired a new ultra-centrifuge, and I searched online for an owner's manual. I found a link to the Cornell web site on the damage that an ultra-malfunction can do to a lab. I emailed my boss the link, and used the subject heading "Ultrafuge explosion".

A few minutes later, he came flying into my office and started screaming at me "NEVER send me an email with that subject line again!" Apparently, he had mistaken the subject heading as the entire message and ran to the lab to survey the damage...