From an article on magician Ricky Jay:
I once asked Mamet whether Jay had ever shared with him details of his childhood.
Mamet replied, “I can’t remember.”
I said, “You can’t remember whether you discussed it or you can’t remember the details?”
He said, “I can’t remember whether or not I know a better way to dissuade you from your reiteration of that question without seeming impolite.”