“Do they float?”
“What if I stuck a pin in them?”
One more stupid thing people ask big-breasted women…
If you can touch them, they are real. 
I remember a conversation that Charade had overheard while she was playing slots in Atlantic City last year. A man and a woman were playing a pair of slot machines beside her and she overheard the woman ask him if he thought her tits were real. The woman had replied that they were too big to be real. When Charade related the story to me, she had been worried that they had realized she was stuffing. I laughed, and told her that I was quite sure the woman had assumed that Charade had had implants, not that she was stuffing her bra.