MSNBC asked for examples of practical jokes, and one viewer told the story of a fellow worker who was proud of the gas mileage on his new car. So the co-workers started adding small amounts of gas while it was parked in the company garage. The mileage kept getting better. Then after taking the car in for a routine checkup at the dealer, the co-workers started removing gas. Now the car owner is sure the dealer screwed up his car. Ha ha!