Other epochs have given us memorable heroes: Spartacus, John Wayne, and Horatio Alger. Our own could be remembered as the age of the loser. The American cinema of mumblecore, Judd Apatow, and Noah Baumbach is enamored with characters — mostly male — who seem too feeble, weak-willed, and pathetic to hang an entire story on. But they end up stealing the show, often proving nearly triumphant in the end with the babe on their arm and self-respect oozing from their pores. Once upon a time, losers were the province of Woody Allen or Martin Scorsese; now everyone’s in on the downtrodden game.

In Cyrus, John (John C. Reilly) is yet another classic 21st century cinematic sad sack. How sad is John? While other Los Angelenos are out partying, he’s at home masturbating. His idea of an opening line to a woman at a party his ex-wife Jamie (Catherine Keener) drags him to is “I’m lonely, depressed, borderline desperate.” Women, naturally, flee from his dark mood and a countenance that sits somewhere between a ’40s pugilist and Frankenstein’s monster.

Like a gift from heaven, John’s seven-year losing streak appears to be over when he meets certified babe Molly (Marisa Tomei) at the party. She adores him despite the fact that he’s such a dolt (or perhaps because he is). Turns out she has her own overgrown baby at home, 21-year-old Cyrus (Jonah Hill), who hasn’t yet flown the coop, and, in the process, he seems to have developed into his mother’s substitute boyfriend. Something deeply, disturbingly Freudian is going on in this dark comedy, which dwells in the dank, cave-like zone where humiliation and hatred reside. Both anxious to be the other man in Molly’s life, John and Cyrus begin a covert war of the wills to win her affections.

Overweight and frighteningly intense, Cyrus is an aspiring techno-composer. In one of the film’s funniest scenes, Cyrus plays John some of his music in his living room “studio.” He fixes John with a stony expression and proceeds to bang out his synthesized whale-sound opus, his gaze never leaving John, demanding a response. Like most of Cyrus, the scene is both skin-crawlingly excruciating (we’ve all felt trapped by politeness into appreciating someone else’s dream/artwork/family melodrama) and quietly hilarious. John plays along, bopping his head, offering a thumb’s up. But when Molly enters the room, she’s really into it, an adorable middle-aged raver getting down at the disco-built-for-two where Molly and Cyrus, metaphorically, dwell. Mother and son are deeply on the same wavelength and the idea is in some ways sweet, evidence of the depths of maternal devotion.

But for the most part, directors/writers Jay and Mark Duplass (The Puffy Chair) instead show that bond as profoundly icky in terms of its Oedipal heebie-jeebiness. Directors associated with the mumblecore movement, which is full of halting, awkward human conversation and fly-on-the-wall authenticity, the brothers have created, essentially, mumblecore on a bigger budget (and with big-name actors) for Cyrus.

Reilly has always had a vulnerability and warmth that makes him uniquely endearing. A basically decent, sweet-natured guy, you can see John struggling to stay afloat as he negotiates the strange psychological pit he’s fallen into. Trying desperately not to offend Molly, but also anxious to let her know her baby boy is a psychopath, John becomes a master of diplomatic double-talk.

Cyrus may largely be a joke about the creepiest kid ever, a son that gives even Norman Bates a run for his money, but it’s nevertheless a canny one in treating the land-mine territory of modern family and 40-something romance. There’s some subtext to chew over too, like the shudder-worthy suggestion that the reason John appeals to Molly in the first place is his resemblance to her son. While other women at the party back away, Molly is drawn to John’s aura of despair. His solitude, social retardation, and ineptness are her catnip. A kind of living-room thriller, the film recognizes that more than terrorists, assassins, or psychopaths, it’s complicated human relationships, insecurities, and fears that constitute the most thrilling, tension-generating plot lines of our own lives.

Cyrus is a funny and observant movie, small enough in its ambitions that you can forgive an ending that kind of peters out and a lingering feeling that the real psychological heart of this trio is mostly left on the surface. Perhaps we’ll have to wait for Cyrus: The Revenge.