For all its supposed edginess, “The Overnight” is basically an old-fashioned couples-relationship comedy that hearkens back to 1970s “swingers” farce. Patrick Brice’s film—essentially a four-hander that might have been adapted from a single-set play—is slight and only sporadically amusing, though it does boast a couple of cheekily cheery performances.

The set-up is a simple one. Alex (Adam Scott) and Emily (Taylor Schilling) have just moved to Los Angeles from Seattle with their young son RJ (R.J. Hermes). She’s an executive in some amorphous tech firm, while he’s a stay-at-home dad anxious to meet people. Still, they’re not exactly overjoyed when they’re approached during an outing in the park with R.J. by voluble, over-friendly Kurt (Jason Schwartzman), with whose son Max (Max Moritt) their kid strikes up a quick friendship. But Kurt’s persistent, and though they have some trepidation about doing so, they accept his invitation to pizza night with Max and his wife Charlotte (Judith Godreche).

What transpires over the course of the evening and the following morning—Alex and Emily are persuaded to put R.J. to sleep with Max upstairs while the four adults continue to party—seems on the surface to be a fairly typical seduction of a pair of uptight squares by a couple of wild-eyed swingers. First it’s an excess of booze, followed by drugs, and then the prospect of sexual experimentation. In the course of the conversation, Alex must confront the psychological problem that’s been plaguing his ability to satisfy Emily of late—his obsession with his small penis. But it turns out, as the story grinds to its end, that he’s not the only one with a problem.

“The Overnight” aims to be surprising, even shocking, but in the end it winds up being little more than mildly naughty, drawing titters rather than gasps. But what else do you expect from a picture that uses the same hoary old gag—in which children burst in on parents who are engaged in pleasurable activities under the sheets—not once but twice?

In fact, the only saving grace in the picture involves the work of Scott and Schwartzman—and not merely in terms of their willingness to gamely sport some artificial appendages. Scott is amiably laid-back, but Schwartzman takes charge, indulging his penchant for oddball, over-the-top eccentricity without becoming obnoxious in the process. Kurt’s succession of revelations about himself—his businesses, his hobbies, his modes of child-rearing—are among the script’s strongest points, and Schwartzman puts them across with panache, though one might find it difficult to accept the final twist that brings the evening’s activities to a close. Schilling and Godreche handle their roles well enough, but this is really a story that takes the male perspective more often than not, and treats that of the women with less flair. On the technical side, the picture is a relatively nondescript affair, though there’s some evidence of imagination in the design of Kurt and Charlotte’s hilltop abode (by production designer Theresa Guleserian , shot with apparent admiration by cinematographer John Guleserian).

One of the Dr. Phil-type messages of “The Overnight”—the one that solves Alex’s dilemma—is that size doesn’t matter all that much, and the picture tries to prove the point by clocking in at a mere 75 minutes. But at just an hour-and-a-quarter, it feels not just short but undernourished.