Oh homeschoolers. So awkward in social situations, so pumped-up with their own inflated sense of self. Is it any wonder that calling someone “homeschooled” is now the PC-version of “retarded”? But even the most dense and unaware of them must occasionally have the sense that other people look at them askance. And maybe, as Rob Broadhurst and Brent Black have envisioned in their infectious new musical I’ll Be Damned, some of them are desperate enough for friends to make a deal with the devil.

A friendless graduate of his mother’s tutorials, 19-year-old Louis (Jacob Hoffman) finds himself alone at the birthday party he has thrown for himself. self-involved to the point of blindness, he has alienated his co-workers at a comic book shop with his incessant prattling about his own creation, superhero Friendetta, whose superpower consists solely of finding friends for the friendless. his mother (a manic, hilarious Mary Testa) doesn’t think there’s anything wrong with a mother and son being one another’s BFFs, but louis wants more, like a degree from a “real boy college.” suddenly, everything he yearns for seems within his grasp when Satan himself (Kurt Robbins) shows up at his party, offering him one bona fide bestie in exchange for his mortal soul. Without much debate, louis signs, and the gruesome twosome head off in search of someone who genuinely likes Louis for himself.

The search, as it happens, doesn’t take too long, just an act. The rest of the show revolves around a now damned Louis trying to reclaim his soul, and what was a dark and funny musical turns a bit treacly. Luckily for Broadhurst and Black, they have a secret weapon in the adorkable Hoffman, who imbues Louis with an awkward charm that belies his friendlessness. Breaking into gangly dances or guffawing with his mother over silly jokes (Hoffman and Testa’s chemistry should be bottled and sold), Hoffman sells the material with a winning nonchalance.

Also due for his share of praise is Robbins. Singing the hell out of the devil’s songs, Robbins reminds you of what musical comedies used to be like, before re-imaginings (which gave us the vocally wan Douglas Hodge in La Cage aux Folles on Broadway) and star casting (which gave us Sean Hayes’ strained warblings in Promises, Promises). Robbins has the kind of powerful voice that you didn’t even know you missed until you hear it. Testa, however, often covers up her rough vocals with tricks and tics, going for laughs instead of the notes. It’s a disappointing distraction from an otherwise funny and moving performance, one that director April Nickell should have nipped in the bud.

The supporting cast all have their chance to shine, with varying results. Alison luff and Gregory Treco are standouts, but Kenita R. Miller is underwhelming as Friendetta. She can’t quite overcome her character’s bland dialogue and unflattering costume (from hit-or-miss designer Andrea Varga, whose reliance on Hot Topic for demon costumes is vicariously embarrassing), and her scenes generally end awkwardly.

What does it matter, though, when Hoffman and Testa are giving us one of the funniest and most painful mother-son relationships yet portrayed on stage? Louis wants a friend, but his mother already has one: Louis. And Testa is heartbreaking as she slowly realizes that Louis needs more than she can provide for him, even with her macaroni Mondays and the promise of four years of home-schooled college. I’ll Be Damned might be a funny musical about the meaning of friendship on its surface, but there’s a darker story of a mother and son’s bond that propels the show just beneath.

>> I’ll Be Damned

Through July 18, The Vineyard Theatre, 108 E. 15th St. (betw. Irving Pl. & Union Square East), 212-868-4444; $18.