with truly sensational breasts. After they have both been drinking pretty heavily, he tells her he is a physician and he has learned the human body and all its tricks.
She ask what kind of body tricks is he talking about.
He says that, for example, he can tell her what day she was born just by examining her breasts very carefully.  
This amazes her and she tells him to go ahead.
He unbuttons her blouse and starts fondling her breasts.  
After about 5 minutes she says to him:
OK can you do it? Can you tell me what day I was born?"
"Sure" he says.
"Ok, when was I born?"
"Yesterday."