A man is walking home one night when a woman stops him and says, "twenty dollars." He had never been with a prostitute before, but he decided to do it.

They are going at it for a minute when all of a sudden a light flashes on them.

“What’s going on here?” asks a police officer.

“I’m making love to my wife,” the man says.

“Oh, I’m sorry,” says the cop, “I didn’t know.”

“Neither did I until you turned on that light."