After IPOing, with so much Bob Pisani fanfare, RenRen, has just forced the SEC to activate Short Sale Rule 201, having plunged from $22 yesterday to below $16 today, and just $2 away from its IPO price, which at this rate will be taken out shortly. Somehow we doubt the CME will hike "overvalued Chinese stock" margins today. Still, we wonder if the Chinese IPO bubble finally over? And as for RENN, who would have thought a company IPOing at 72x sales may be poised for a collapse. In other news, is the "market contingent" LBO of the NYSE by the Nasdaq now pulled?