Imagine yourself transported to a parallel universe, a bizarro world, where the hip culture listens not to rock 'n' roll or R & B but to polka music, which is considered sexy and dangerous. That's the kind of world Brave Combo would fit into perfectly, being the oddballs they are in this world. What's especially endearing about these masters of rockin' polkatharsis is that they take on their chosen repertoire (which also includes cumbias, schottisches, waltzes, etc) without condescension--that is, without feeling compelled to treat accordions as a camp joke. They play this music, if not with absolute "authenticity," certainly with power and genuine affection (and plenty of Nino Rota eeriness). So whether you are hip or square, or maybe a little bit of both, Brave Combo wants you to put down that ginger ale and get out on the dance floor. You can wait until later to reflect on how weird they are. Wednesday, FitzGerald's, 6615 Roosevelt, Berwyn; 788-2118.