Not my prank but one done by one of my old shooting buddies in the early 70's. He was a city fireman and worked in an auto parts store on his days off. Next door was a Buick dealership. The auto parts owner bought a Buick with a huge V-8 from the dealer next door and noticed that the gas gauge barely moved as he drove for several weeks. This was before people were concerned with MPG but he started tracking his and bragging about it to anyone who would listen. That was until he took it in for it's first oil change and check up then the mileage dropped drastically. He was so upset with the dealer demanding to know what they had done to his one of a kind engine. Before it got too far out of hand, his employees fessed up that they had been adding gas to his tank until the first service, then syphoning gas out afterwards. No one was fired but he was pissed for sometime then finally admitted it was one heck of a prank.
