The film theorist Stanley Cavell liked to write about something he called the “remarriage comedy.” The definitive films in that genre included His Girl Friday, The Philadelphia Story and especially The Awful Truth, and they involved couples that had begun to doubt the viability of their relationships. The narrative charted an arc that involved their decision to separate as well as their realization that they wanted to be together — a reaffirmation of their commitment to a loving relationship.

Mr. and Mrs. Smith, written as a thesis screenplay by Simon Kinberg when he was a graduate student at the Columbia University film school, very obviously wants to be a remarriage comedy. John and Jane Smith pretend to lead average lives as well-traveled corporate flunkies who retreat to a well-appointed home in the New York suburbs. In reality, they’re both well-traveled corporate assassins — but it’s a secret they keep from one another. (The exact nature of their employment is kept from the audience. You may be inclined to wonder what kind of murders a private-sector assassin might be performing on behalf of big tobacco or maybe the military-industrial complex, but this film takes no steps to elucidate. If Kinberg ever had satire on his mind, it’s been leached out of the proceedings.)

Once the two of them figure out that they’re in the same business, and that the other is a dangerous rival, they engage in a War of the Roses-style domestic struggle — gunplay as an unsubtle metaphor for marital discord. Brad Pitt and Angelina Jolie exude movie-star charm and sex appeal; their mere screen presence in such a scenario borders on broad comedy. But it wouldn’t be enough for a summer blockbuster to merely update the screwball comedies of the 1930s and 1940s with a couple of highly charismatic star leads. So Mr. & Mrs. Smith takes as many cues from dumb American action movies as it does from classic Hollywood. The result is a preening, superficial film that expects you to appreciate its smart concept without noticing the stupid execution — too awkward to work as a thriller and too swollen with action to cohere as romantic comedy.

I’m not saying that Mr. & Mrs. Smith never brings the funny, and the first half of the film is intermittently as amusing as it is dopey. For instance, I laughed out loud during a dinner party sequence early in the film that has one harried neighbor hand Jolie a baby with a full diaper — the baby stares and smiles at her as she reacts with unveiled disgust. Sure, it’s funny, but it’s also a Screenplay 101 character note that the movie never expands upon. The big action centerpiece that has Jolie blasting holes in the wall with an assault weapon as she and Pitt stalk one another through the Smith family household, making a shambles of the place in the process, is a hoot. Pitt, especially, can be hilarious, and Liman has a pretty good ear for the interplay between his characters. But the second half of the film, one smugly implausible action set piece following another, never has time to follow through on any of its set-ups.

And who are these people, anyway? Mr. & Mrs. Smith has neither the time to present its protagonists as the loving couple it believes them to be or the nerve to portray them as the charming psychopaths that they certainly are. The Smiths finally learn how well they function as a team only when they’re boxed into a corner of an upscale home-furnishings superstore and have to take out a small army of assassins with a full arsenal of slo-mo acrobatics, pumping heat out of both fists. There’s a tongue-in-cheek ridiculousness to this that John Woo could have milked to melodramatic effect, but in director Doug Liman’s hands it falls flat. It merely culminates a succession of dull set pieces that add up to an exercise in slick target marketing — a violent fantasy for insecure yuppie couples seeking aggrandizement.