After last summer's Assassins, Mario Cantone is back on Broadway with Laugh Whore, a one-man show full of cracks on past projects but not a peep about his stint on HBO's Sex and the City. Whore is produced by HBO rival Showtime...could that explain the lack of Sex talk? ''It was a great experience,'' says Cantone of his role as Charlotte's ear-splitting wedding planner. ''It was kinda too perfect to be funny.'' Dang. We wanted dirt!