This guy walks out of a bar. It's a dark night, and he hears a lady whisper "30 dollars" from the shadows... The man has had a few beers and thinks to himself "I've never been with a prostitute... Why not?" He scurries into the bushes where he'd heard the voice with 30 dollars in his hand and starts having sex. Along comes a policeman and shines his light on them.
"Hey, what are you doing over there?"
The guys from the bar says, "Sorry officer, just having sex with my wife"
"Oh, sorry," replied the officer. "I didn't realize it was your wife."
And the guys says, "Neither did I til you shined your light on us!"