At some point in Jackass 3-D, maybe when you’re trying to suppress the gag reflex while watching thirty pounds of feces being hurled in three dimensions across the theater, it will occur to you: What the hell did I expect? “Jackass” is a ten-year running gag for Johnny Knoxville and his pack of adolescent-minded pranksters with penchants for sack taps and surprisingly few permanent injuries. And yet the concept and its iterations can still make you wince. It’s like a great big live-action Roadrunner cartoon- “I’m convinced when Knoxville watches Tom and Jerry, he thinks he’s watching reality television,” director Jeff Tremaine said in a recent interview- but the colossal smashes are live, too. And far more painful. There are plenty of gross-out moments in “Jackass”, and we don’t recommend that the queasiest of stomachs waste their money on popcorn for the show. But those moments are rarely funny, and much more often simply inspire the kind of can-you-stand-to-watch-it posturing among its audience members. By far the most successful gags in “Jackass” are the physical ones, the moments of pure heart-stopping pain for cast members dressed as lion tamers, superheroes and musicians in a marching band. The best moments are those with smirky nods to pop culture. One of the more inspired sketches is a spoof on the old Maxell commercial “Blown Away Guy”, depicting a man and his martini being literally blown away by the force from his stereo speakers. Recreating the setup with armchair, sunglasses and booming rendition of “Ride of the Valkyries”, the camera pans out to reveal the real source of the wind: a jet engine parked 20 feet away. Like its two-dimensional predecessors, “Jackass” is a disjointed and cheery mess of ensemble performances, commandeered but not controlled by Knoxville. The opening and closing sketches are particularly fantastic. Your best bet is to admit a night of regression and laugh as hard as “Jackass” wants you to- if only for the fact that it’s not you who just got kicked in the face by an NFL player.