Cheer and moaning in L.A.

Kenneth Branagh once said in a movie many years back: “There is no such thing as grown-ups, they’re only children with money.”

Now Branagh is playing just the sort of dastardly kind of grown-up he once criticized, and with obvious relish, in “How to Kill Your Neighbor’s Dog.” As an immature, snide British-American playwright named Peter McGowan, Branagh excels in sarcastic rejoinders and mean-minded bons mots. Whining and complaining dribbles constantly from his mouth like pureed spinach from the spoon of a colicky 2-year-old.

If you’re looking for a thoroughly unpleasant specimen of middle-aged manhood gone sour, the search ends right here: “How to Kill Your Neighbor’s Dog” will have you fighting back the urge to march up to the screen and flatten Peter’s nose with one good jab from the left. In fact, the title is downright misleading unless director Michael Kalesniko intended the dog to mean Peter. Let’s leave the dog alone; the playwright definitely has more problems.

And really, is there no God? That may sound like a non sequitur, but wait till you hear how Peter lives in this splendid, many bedroomed house in a Los Angeles suburb and is married to a beautiful, angelic dancer who, with a permanent smile, puts up with his idiosyncrasies.

How this wife, Melanie, wound up marrying such a pain in the lower extremities is a gaping enigma, especially when she looks like Robin Wright Penn and obviously could have partnered anyone she chose. With an indulgent smile and kind eyes, she says, “Baby! You’re such a baby!” to her pouting, chain-smoking, wine-sodden husband. “Ha!” he says. When he accompanies Melanie to the gynecologist’s for a pregnancy check-up, he observes her stretched out on the examining table, lights a cigarette from what appears to be sheer boredom and remarks casually: “Why is it that a woman’s gateway to heaven is located so close to the . . . ?”

To cut Peter some slack, the past couple of years have been tough for the guy. Once the talented and darling author of hit plays (“To think that I was once working with Jason Robards!”), his career has slid toward obscurity after a run of bombs at the theater box-office. He has writer’s block and insomnia — from the consistent yapping of a neighbor’s dog. He has a stalker (played with hilarious abandon by Jared Harris) prowling the area and introducing himself as Peter McGowan.

To cap it all off, his wife desperately wants a baby, but he can’t stand the thought of little pattering feet disrupting the sanctum of his large, tastefully decorated study. That’s where he hastily retreats (wine bottle in tow) when his wife gleefully makes friends with — and then brings over — 8-year-old Amy (Suzi Hofrichter), who just moved into the neighborhood with her mother. Amy had cerebral palsy, which has left her legs shaky and uncoordinated — and because of this she’s somewhat ostracized by her peers.

To cover up her insecurities, this girl has developed a cranky, saucy character that’s an excellent match for Peter. The pair begin to associate with each other, initially with enmity but later with genuine camaraderie. And Peter comes to realize how much he has been cut off from real conversations between real, living people, and the extent to which he had been immersed in the excessively cold and cynical dialogue of his fictional characters.

Michael Kalesniko filmed this movie in 1999 and it bounced around for a while on the film-festival circuit (to general applause). But for unexplained reasons it went into hibernation until 2002 before it finally hit U.S. theaters. Watching it now, there’s a strange serenity and innocence to the story : L.A. suburbia isn’t drawn with the subtexts of boredom and dirty secrets, the sky is gorgeously blue and as Melanie blithely tells Amy: “You can come on over any time — we always leave the gate unlocked!”

Come to think of it, how many single moms today would entrust an 8-year-old to a strange couple she just met? And the very fact that Peter is actually permitted to smoke a lot says something about how things things have changed. Five years ago, some critics described it as a “dark comedy,” but no matter how caustic Peter’s statements get, there’s nothing dark about the sunny optimism and inherent goodwill that shines through the entire movie.

With its snappy dialogue and tart wit, “How to Kill” is something Woody Allen may have made, and you almost expect to see Peter don an oversize tweed coat (incidentally, Branagh did play Allen’s alter ego in “Celebrity”). But the character of Melanie couldn’t exist on Planet Allen. A wife who doesn’t philosophize, doesn’t unleash her inner turmoils, doesn’t need a shrink, smiles all the time and looks gorgeous? She belongs in Hollywood.