[JoeT]

my dad had a diesel ford escort in the 80's. He was always boasting to my brother and I about the great gas mileage he was getting.

We decided to "Ef" with him. One week we'd add 5 gallons of diesel and added to his tank...he went around telling us he was getting over 80mpg. a couple weeks later we'd siphon 5 gallons out and he'd freak out because he was only getting 20mpg.

We did this to him for months, until mom told him what we were up to... he was less than amused.