A prominent real estate bigwig caused a stir Thursday by admitting that the New York City residential property market is a big bubble waiting to pop. "If real estate was a publicly traded company and I could short its stock, I would very happily short 57th Street," said Ofer Yardeni, CEO at real estate development firm Stonehenge Partners, referring to the stream of high-end towers popping up along 57th St.'s "Billionaires' Row."