Carter (Adam Scott), right, must manage divorced parents Melissa (Catherine O’Hara) and Hugh (Richard Jenkins) in “A.C.O.D.” (Photo by Quantrell D. Colbert – © 2013 - Film Arcade)

The comedy “A.C.O.D.” opens on what looks like an early-1980s home movie. As a 9-year-old boy is about to blow out the candles on his birthday cake, he hears, just off camera, his bickering parents (Richard Jenkins and Catherine O’Hara, screeching at each other like they’re rehearsing “Who’s Afraid of Virginia Woolf?” in front of a live audience). The look on the kid’s face — almost as painful as it is funny — suggests that this is not the first party they’ve ruined.

Like that resurrected footage, which suggests an old wound that keeps getting picked, long-buried hurt keeps breaking through the humor of this sharp and insightful little film, tearing small holes in its veneer of comedy and adding depth and texture to its superficial jokes.

The film revolves around Carter (Adam Scott), that little boy from the opening scene, now grown and classified as an A.C.O.D. (Adult Child of Divorce) by the self-help writer (Jane Lynch) who used his story as fodder for a bestselling book. On the surface, everything is fine in Carter’s life. He’s got a great job running a hip Atlanta eatery. His girlfriend of four years, Lauren (Mary Elizabeth Winstead), loves him. And over the years, he’s been able to keep his long-divorced but still-warring parents, Hugh and Melissa, from killing each other.

That facade of stability begins to crumble when Carter’s younger brother, Trey (Clark Duke), announces his engagement to his girlfriend of four months, Kieko (Valerie Tian), and his intention to invite Mom and Dad to the wedding. Actually, it’s Carter who has to do the inviting. As he was when he was a child, Carter is still very much caught in the middle. He’s a 9-year-old trapped in a grown man’s body — chronologically an adult but still very much a child.

The set-up is familiar from such films as “It’s Complicated” and “The Big Wedding.” Hugh has had a succession of trophy wives, culminating in a harridan played by Amy Poehler (Scott’s “Parks and Rec” co-star). Melissa has remarried, too, to a guy made stolid by long suffering (Ken Howard). And even though Hugh and Melissa can hardly stand to be in the same room, there’s the implication that they may not exactly be over each other.

I know: not exactly fresh. Still, Jenkins and O’Hara almost make it work.

A better question is whether Carter — who’s justifiably commitment-shy — and Lauren will marry or break up. But the film’s most interesting narrative arc concerns Carter’s emergence from the protective emotional cocoon he’s developed as a result of his parents’ toxic relationship.

The cast is uniformly strong, with standout performances from Lynch, O’Hara, Jenkins, Poehler and Howard. Jessica Alba also makes a nice, if brief, appearance as a fellow child of divorce with whom Carter almost cheats on Lauren. And Winstead brings surprising depth to a small role, in which she has little to do except wait for her boyfriend to grow up, or to at least let go of his cynicism about love.

That’s pretty much what we’re waiting for, too. Will Carter and Lauren end up happily ever after? What about Trey and Kieko? Hugh and Melissa?

Written by television veterans Ben Karlin (“Modern Family”) and director Stu Zicherman (“Six Degrees”), the script doesn’t exactly deliver the happy ending that we’ve been conditioned to expect by a steady diet of sitcoms and movie comedies. Judging by the groans at a recent screening, the film’s open-ended conclusion left many in the audience feeling cheated of the closure they felt they deserved.

This spontaneous reaction was, for me, the most interesting thing about the film. By the standards of traditional romantic comedy, “A.C.O.D.” may leave a slightly sour aftertaste. As a look at the state of modern monogamy — or at least our enduring if misguided faith in it — it’s refreshingly acerbic.

★ ★ ½

R. At Landmark’s E Street Cinema. Contains obscenity, drug references and a sex scene. 87 minutes.