One of my friends told me about a practical joke he played in high school. He read that car manufacturers made more cars than car keys; therefore, it was possible that your key might work for a car other than yours, if it was the same make and model. He drove a common Japanese import and thought his high school's parking lot would be a good place to see if what he read was true.

During lunch one day, he went to the parking lot to try out his key on other cars. Sure enough, it worked on another car. What did he do next? He moved the stranger's car to another parking spot two or three rows away. A few days later he moved the stranger's car again. This time he found a much better parking spot for his foil.

My friend stayed after school and waited to see something he would one day tell his son about. He recognized the bewildered man who paused where he thought he had parked his car. It turned out to be the geometry teacher who was famous for terrorizing students.

Slappy, the patron saint of practical jokes, works in mysterious ways.

The geometry teacher went from bewilderment to anxiousness to outright panic, and then sprinted back toward the school when he ran into his car, literally.

The best practical jokes have both a sense of restraint and a sense of whimsy. They can be more involved than the D-Day invasion, such as the case of the MIT students who took apart a professor's car and put it back together on the roof of a building.

Good practical jokers are like jewel thieves. They slip in under the cloak of darkness and leave neither clues, fingerprints nor business cards. Unlike other artists, practical jokers have no interest in being recognized for their work. Anonymity is as important in practical jokes as it is in crime fighting. Illusion is the raison d'etre of practical jokes.

Practical jokes often require convincing people that something exists when it doesn't. An example of this is the state of North Dakota. All maps of the United States include North Dakota and most Americans have heard of it. But do you know anyone who has actually seen it? I've called North Dakota a number of times and nobody's ever answered.

Other practical jokes try to convince people that something doesn't exist when it really does. To quote Verbal, that merry prankster from the movie, "The Usual Suspects," "The greatest trick the devil ever pulled was convincing the world he didn't exist."

Don't tell me the devil doesn't exist. I know better. He was my geometry teacher.

You may be wondering if car manufacturers actually make more cars than keys. I don't know. I also don't worry about it. I drive a car hardly anyone else drives. I drive a Ford.