ZeroHedge IRS Takes Aim At AQR's Tax-Slashing "Holy Grail", Warns Crackdown May Be Retroactive For three years Wall Street's hottest product wasn't a stock, a sector or even an AI trade - it was losing money (it in a very precise, very engineered way so "losses" could be handed to the IRS while the portfolio kept compounding). But the taxman has finally…