Your best practical joke?

[DeputyUICHousto]

I love to have my rookie partner go to the store to buy a watch for timed games. But he has to get a special "umpire" model. "Afterall, you can't have players and coaches know how much time is left in the game. You have to talk to the store manager because these watches can't be available to the general public."

Obviously, the store manager has no idea what this guy is talking about.