"How to tell if she's a virgin" joke

A fellow talking to his friend says, "How can I tell if my girl is a virgin?"

Friend tells him, "You have to wait till you wedding night, you show it to her and ask what it is. If she calls it a penis, she's a virgin. If she says it's a cock, she's been around."

So the guy gets married, and in the hotel room he flips it out to her and says "What is this?"

"That's a penis!" she replies.

"Great," he sighs, "I thought you were going to call it a cock."

"Of course not! A cock is twice as big!!"