Pershing Square Capital Management chief Bill Ackman appears to be not just short Herbalife’s (HLF) stock. He is the short. At least, that’s what we can infer from Ackman’s Thursday comment that Pershing is short more than 20 million shares. Herbalife’s short interest was near a record high of 22.2% this week, according to Markit data, or somewhere around 24 million shares. That would suggest Pershing is 80% or more of the market’s entire Herbalife short. This is where it gets interesting. By taking such a huge position in what happens to be a pretty small supply of stock, Ackman may be making it tougher to achieve his ostensible goal in going so public: Convincing other investors to go negative.