When we popped into the Museum of Sex last night for a preview of their new exhibit on erotic outsider art, we didn’t expect to find a discotheque on the premises. But there it was: An exhibit titled “Night Fever” has brought a massive Richard Long Audio System (the type used at Studio 54 and Paradise Garage) to MoSex’s bar space, and it’s absolutely killer. Back when we visited MoSex for Kayvon Zand’s sadly short-lived weekly, the bar had a fusty library look, with couches set between bookcases. But Jason Volenec, designer of atmospheric restaurants like Miss Lily’s and Tertulia, has given it a ‘70s vibe via silver-foiled walls (a la Warhol’s factory), disco balls, and swiveling glass coffee tables.