October 20, 2004 THAT PORN-AGAIN L.A. LOOK ONE of the biggest laughs at the HBO screening of “Thinking XXX” came when John Waters said, “In New York, nobody looks like a porn star, but in L.A., everybody looks like they could be one.” Along with Waters, the documentary by photographer Timothy Greenfield-Sanders features porn stars as they stripped and posed in Tim’s Lower East Side studio for his book, “XXX: 30 Porn-Star Portraits,” plus commentary from Gore Vidal, Michael Musto, Nancy Friday, Karen Finley and Faye Wattleton. After the screening at HBO headquarters on Sixth Avenue, folks like Mary Boone with Dr. Dan Baker, Lou Reed, Rocco DiSpirito and Norman Pearlstine mingled with porn stars Heather Hunter, Savanna Samson, Gina Lynn, Chad Hunt and Michael Lucas. Some fans gathered autographs, having the performers sign their portraits in the book.