Perhaps it’s appropriate that a movie about infidelity should be faithless to its audience, but that doesn’t make “The Dilemma” any more enjoyable. Ron Howard’s misfire is being marketed as a wacky buddy farce, but it’s actually a dismal dramedy in which the comic bits aren’t funny, the more serious parts heavy-handed and contrived, and the scenes that try to mix the two tonally muddled. For Howard, it seems the need to juggle the picture’s disparate elements was a dilemma he couldn’t solve.

Vince Vaughn plays Ronny Valentine, a motor-mouthed fellow who’s the aggressive salesman half of a partnership with his long-time engineer pal Nick Brennan (Kevin James) in a small Chicago engine-design company. (As is so often the case in such movies, their friendship is totally implausible, and the attempt to show them as close never convinces.) Nick’s married, apparently happily, to Geneva (Winona Ryder), while Ronny is finally getting serious about proposing to live-in girlfriend Beth (Jennifer Connelly)—something Nick’s encouraging him to do.

But just as the duo win a development deal with the head of Chrysler (Chelcie Ross) to develop an electric engine that will simulate the sound of a muscle car (thereby replacing air pollution with noise pollution—just one of the many idiocies in Allan Loeb’s script), Ronny stumbles upon Geneva making out with a young stud (Channing Tatum) in the botanical garden he’s scoping out as a place to propose to Beth. (A likely coincidence, of course, since Chicago is such a small town and a public garden is the logical place a couple would go to frolic and snuggle.)

Ronny’s problem, of course, is whether to tell his buddy about his wife’s dalliance at a time when his stressed-out partner is trying to complete work on the engine that will make or break their company by the (completely arbitrary) deadline. The matter’s complicated by Geneva’s refusal to come clean with her hubby, her insistence that Nick’s no angel himself, her threat to reveal an early indiscretion between her and Ronny to Nick (and lie about his supposedly continuing advances), and Ronny’s attempt to get incontrovertible evidence of the extramarital affair. The poor fellow’s clumsy efforts endanger his relationship with Beth, of course.

Many of the sequences in “The Dilemma”—like those between Vaughn and Ryder—are played like high drama. Others go for farce, like the one in which Ronny discovers Geneva’s infidelity while thrashing about in a bed of poisonous plants (and suffers a host of symptoms as a result, though that’s quickly dropped after extracting a few gruesome jokes from the idea), or the confrontation between Ronny and her lover in the guy’s apartment, which is meant to be dark slapstick but comes off as simply nasty. Neither element works. But worse than either are the moments that strain for a blend between the two, for example the long monologue that Vaughn delivers as Ronny’s toast to Beth’s parents on their wedding anniversary. It’s meant to provide the actor with one of the stand-up style rants he’s famous for, but is so badly written that it’s embarrassing not merely for the character (as intended) but the actor as well (not). The same could be said of the intervention sequence near the end (staged in response to Ronny’s gambling addiction—a condition that’s introduced abruptly precisely to allow for the scene), in which the only actor to emerge with his dignity intact is Troy West, who brings an amusing befuddlement to the group leader.

These are only two of the instances in the movie in which Vaughn has to endure humiliation, either physical or psychological. He throws himself into them, and everything else the screenplay demands of him, with his usual manic energy, but in this case it’s in a lost cause—the result is exhausting rather than exhilarating. As for James, it’s a continuing question why such a dull, unfunny person continues to be cast in these comedies—chubby comedians are always in demand, but he’s a boring, inert presence who’s even worse when he tries to cut loose (as in a dance sequence). Connelly is totally wasted in a thankless role, but Ryder shows some fire as the unpleasant Geneva; it’s nice to see her remaking her career. Tatum is ill-at-ease in a part that feels like it was written for somebody like Seann William Scott. Queen Latifah shows up briefly as a Chrysler executive. Apparently Loeb and Howard decided that their movie couldn’t do without a smart, feisty black woman, so they simply inserted one and enlisted Latifah to do her brassy shtick. It’s tokenism by any other name. And Howard continues his penchant for nepotism by casting dad Rance and brother Clint in minor roles.

On the technical side things are just adequate, with Salvatore Torino’s cinematography taking little advantage of the Chicago locales, except for the obligatory skyline shots. But one can understand why the crew wasn’t particularly interested in doing their best for such inferior material.

Since the theme of “The Dilemma” is the importance of honesty, a critic is only following its injunction by saying it isn’t any good. And though the studio might be hoping that Vaughn might be enough to sell it, the subplot about gambling encourages one to observe they shouldn’t bet on it. The character Tatum plays here, incidentally, is called Zip—which is as much entertainment as “The Dilemma” offers.