Yeah, my definition of a good prank is one where there is no permanant harm done.
Leaving the escort's phone number on his work message slot- funny. Having a female co-worker write it down and put it into his jacket pocket so his wife would find it- not funny.
Most of our pranks are IT related. Disconnect his floppy drive, install another floppy inside the case of his computer. Watch him squirm as he tried to figure out why he is getting inaccessable boot device.
Or once we put another hard drive into the guy's PC and had it boot into Windows 3.11. Just so you know, Windows 3.11 takes about 3 seconds to start up on a Pentium 4 computer.