Joe is having a drink in his local bar when in walks this 
gorgeous woman. Joe, not being too shy, goes up and sits next 
to her.  He buys her a drink and then another and then another. 
After this and the accompanying small-talk, Joe asks her back 
to his place for a "good time."

"Look," says the woman, "what do you think I am? I don't turn 
into a slut after 3 drinks, you  know!"

"OK,"  replies Joe, "so how many does it take?"