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.