Who was Carly Simon thinking about when she wrote "You're So Vain"? Mick Jagger? Warren Beatty? Cat Stevens? The Fab Five? Well, the 58-year-old singer is ready to spill the beans — to the highest bidder, that is. According to People, Simon plans to auction off the answer to raise money for Martha's Vineyard Community Services. Naturally, there's a catch: The winner has to sign an agreement never to tell anyone.