Socially maladroit John (John C. Reilly) is lucky to have an ex-wife as sympathetic as the woman played by Catherine Keener in Cyrus. His ex is so caring that she invites him along to parties with her fiancé and encourages him to strike up conversations with beautiful, single women.

John strikes out again and again. He probably hasn’t dated since Reagan left Washington and has forgotten what to do. But while relieving himself in the bushes, John discovers his soul mate, Molly (Marisa Tomei), a woman who shares his love for Human League synth pop and probably hasn’t dated since the first President Bush.

They are a fun couple on the hardscrabble edge of the free-lancing middle class. But no problem, no story. Instead of being half of a couple, Molly can only be one-third of a triangle with her 21-year-old son, Cyrus (Jonah Hill). And no, it’s nothing as luridly tacky as incest. Cyrus has grown too big for his boyish emotional arrestment. Smothered in maternal attention and lacking a paternal role model, he was never given the encouragement, the kick in the rear, to grow up.

At first Cyrus seems cool with mom having a boyfriend, but his passive-aggression is masterfully keyed to Molly’s emotions and his medicated-looking expression of calm acceptance conceals an angry smirk. The comedy by writer-directors Jay and Mark Duplass—often filmed up close and personal as if through the world’s best cell phone camera—isn’t consistently hilarious, but rather it builds from many moments of situational (and not far-fetched) humor. Could Molly have been attracted to John because he suggests an older, less dysfunctional Cyrus?

The comical scenario has teeth in a postmodern society where growing up and independence are often postponed. While some kids flee back home because of the bad economy, others never seem eager to leave the nest at all. Perhaps it’s the unsettling feeling that those cozy, secure memories of childhood can never be replicated? Maybe it’s the realization that adulthood isn’t so hot in a world of outsourcing, downsizing and social and ethical uncertainty. Or could it be that some parents just enable their children to remain kids forever?

Cyrus is screening at the Oriental Theatre.