"Who's Wife?" joke

A guy on a date parks his car and gets the woman in the back seat. They make love, but the woman wants it again and the guy complies.

She wants more so they do it again, but she still wants more.

Exhausted, the guy says, "Excuse me a minute, I have to relieve myself."

While out of the car he notices a man half a block away changing a flat. He asks the man, "Look, I've got this gal in my car and I've given it to her four or five times and she still wants more. I'll change your flat if you'll take over for me."

So the man agrees & gets into the car. He is just getting into "high-gear" when a cop knocks on the window and shines a light on them. The cop asks, "What are you doing in there?"

The guy says, "I'm making love to my wife."

The cop asks, "Why don't you do that at home?"

The guy answers, "To tell you the truth, I didn't know it was my wife until you shined the light on her."