A guy took his girl out parking in his 4-wheel drive truck, but couldn't convince her to make it because she was afraid that someone would see them. Finally he hit on the great idea that they could do it under the truck where they couldn't be seen. This seemed to be OK with the girl, so they really went at it under the truck. Soon a policeman tapped the man on the shoulder and said, "Hey, what are you doing?" Our hero never looked up and said, "I'm fixing the transmission."
"Well" said the cop, "I think you had better fix your brakes too, because your truck is at the bottom of the hill!"