re: What's the best practical joke you've ever played?

I college, called up one of the guys in my Quantitative Chemistry lab and impersonated the Chinese "Rab" Instructor/TA on his answering machine. Told him that his "concrusions on rab reports were verry verry simirar to is rab partner Rinda...we would need to taak after crass".

This was back before caller ID...so the guy thought it was legit and was about to crap a brick (since he was actually copying nearly all of his work off of Linda). I was going to play it up to see how he would approach the TA about it...but he started to really panic, so I fessed up.