I will likely never get the chance to use this retort, but it's a great one:
[Conrad] Black needed money. He called several friends in New York.
“Do you think you can get a group of people together if the need arises,” he asked one billionaire, “and get me some funds secured against my property?”
“How much do you want from everyone, Conrad?” asked the businessman.
“About $1m each,” said Black.
There was a pause. “You’re my best friend,” continued Black. “Surely you can lend me $1m?”
“Well, Conrad,” said the man, “what’s my private telephone number?”
“I don’t know,” replied Black. “Why?”
“Well, if I were your best friend, you’d have it.”
above from Tom Bower (who's writing a book on Black) at