Dirty Little World, Aha! Productions, at Viaduct Theatre. They don’t call it a punch line for nothing: the cardinal condition for comedy is that something snaps the tension between the apparent and the actual.

The five comics in Aha!’s eighth revue display wizard timing, interact cunningly, and maintain complete control over their rubber faces. What’s missing from the show’s 16 sketches in Rob Mello’s unambiguous staging are the ironic twists that reverse our expectations and, not incidentally, skewer stereotypes. This gay-themed show skims the surface of such easy targets as humorless lesbians, catty gossips, Christian closet cases, incompetent help-line volunteers, self-hating suburbanites, obsessive office mates, and smug control-freak mothers. It’s familiar territory richly portrayed, but most scenes go nowhere, offering no incongruous juxtapositions, just connect-the-dots caricatures. Mary Buckley and Todd Milliner maintain a creepy Disney-like cheerfulness as trendy parents who try to inoculate their kid against eating disorders, bad body image, incest, sex abuse, and bisexuality. But just when you expect the kid to turn the tables, the scene just stops.

There are a few happy exceptions that root the comedy in character. Milliner and Buckley play a customer and clerk in a produce department who share a wacky epiphany as they reveal their secret dreams, torn right from a bodice ripper. Michael Hampton describes “the girl for me” in such flamboyant terms that he guarantees he’ll never meet her. But overall this gay show doesn’t have the twists to keep it from the straight and narrow.