We're going to be laughing for a long time about the practical joke we played at work last Friday. I started thinking about the term "practical joke" and found this on Wikipedia:
The term "practical" refers to the fact that the joke consists of someone doing something (a practice), instead of a verbal or written joke. A practical joke can be caused by the victim falling for a prank, the victim stumbling into a prank, the prankster forcing a prank on the victim, the prankster causing others to do something to the victim, or even causing the victim to do something to others. Sometimes more than one victim is used.
Hmm...the word victim seems a bit heavy-handed; I prefer recipient or beneficiary.
Here's a great prank, from Improv Everywhere: