A guy sees his buddy in a bar and says, "You're not going to believe this, but I've got a wild nymphomaniac in my car out in the parking lot. She's wearing me out! Can you go out to the car and keep her busy? The dome light is off, so she won't know you're not me!" His friend agrees and goes out to his car.
They climb into the back seat and start going at it. A few minutes later, a cop sees them and starts banging on the window, shining his flashlight inside.
"What the hell do you two think you're doing?" The guy says, "Oh, there's nothing wrong, she's my wife." The cop says, "Oh, sorry, I didn't know."
The guy says "Neither did I until you shined that light in here."