At any gym, you can bulk up to the point where it looks like you could kick ass, but what happens when stuff goes down, and you realize yeah, you really do look like you can kick ass? For a gym that actually makes you dangerous, check out Knockout Zone.
Knockout's a not-too-grimy, not-too-shiny multi-disciplinary combat gym run by a multi-disciplined fighting vet (Argentine champ in boxing, kickboxing, full-contact karate), with bags aplenty (30 heavies, two double-ends, speeds, uppercut & knee), a mat area for grappling, and for MMA work, a half-cage...so, a quadragon? Western ass-kicking includes boxing taught by a former Argentine Olympic coach, MMA from a dude who's 10-0 in the octagon, and wrestling coached by a guy who grappled for Wisconsin, where he became a master of the cheesehead-lock. Eastern disciplines include knee- and elbow-intensive Muay Thai kickboxing, standard kickboxing, Brazilian jujitsu instruction from a former three-time world champ, and a Filipino martial art specializing in knife and stick fighting called Kali/Escrima, which is also the cause/effect of getting your heart ripped out in Temple of Doom.
If you're afraid of even pretend-fighting, they've got free weights, mad Cybexes, a spinning room, boot camp circuit training with tires, sandbags, and sledgehammers; there're also some non-traditional amenities, like an outdoor patio with a projection screen for PPV MMA/boxing matches, and a wifi'd cafe complete with beer & wine -- the surest route of all to thinking you can kick ass.