The producers of Forever Plaid claim their show is Chicago’s longest-running musical, but the honor actually goes to Co-ed Prison Sluts. Years before anyone thought of bringing Forever Plaid to town, this raggedy-assed, iconoclastic musical comedy was running in a blues club and then in the Annoyance Theatre’s space on North Broadway. Created through improvisation in the late 80s by a handful of local actors under the direction of Mick Napier, Co-ed Prison Sluts quickly became a hit, reviving interest in both late-night shows and the use of improv for making theater. The show has had a host of imitators over the years, most notably Billy Bermingham’s Cannibal Cheerleaders on Crack, but none of them has been able to reproduce its charming mixture of childlike innocence and adolescent taboo flouting. Even the folks at Annoyance haven’t been able to best it, though God knows they’ve tried. (Having seen the show five times, I’m convinced the secret is Faith Soloway’s songs, which fit hilariously perverse, profane lyrics to tunes so syrupy they could have been lifted from a bad musical for children.) A decade after the show first opened, Co-ed Prison Sluts remains as fresh and funny as it was back in the first hours of the Bush administration. And unlike Forever Plaid, it tells a story that’s complex and fully realized, if a little twisted. Annoyance Theatre, 3747 N. Clark, 773-929-6200. Open run: Fridays-Saturdays, 10:31 PM. $12.

–Jack Helbig