There's a reason that strippers have hard bodies (aside from the fact that most folks wouldn't pay to ogle fat slobs). And the reason is that undressing in front of strangers requires stamina and guts -- well, at least it does at Crunch Gym's "Cardio Striptease" classes. Led by Sergio Novoa, the 60-minute sessions are a workout as well as a dream come true for the uninhibited. Combining R-rated bump-and-grind dance routines -- lots of crotch grabbing and pelvic thrusts -- with basic aerobics moves, "Cardio Striptease" appeals to the exhibitionist in all of us, though most participants come dressed in a few extra layers. (The average female student winds up in a sports bra by the end of class.) Better still, it's an undeniably fun way for men and women to burn calories. At the New Montgomery location, the class is so popular that even its Friday night schedule can't keep 'em away. With a male-to-female ratio of 1-to-5, guys who aren't afraid to shake their fannies and bare all will find themselves in a roomful of sweaty, spandex-clad gym bunnies willing to shed more than just a few extra pounds.