Two students at New York University’s Graduate Musical Theatre Writing Program — Joshua Salzman and Ryan Cunningham — wrote a thesis musical that ultimately played Off-Broadway in 2006. Songs from the show were so popular with San Diego State University MFA students that their teacher, Rick Simas, got a demo recording, which he took to North Coast Repertory Theatre artistic director David Ellenstein. Directed by Simas, “I Love You Because” continues only through Sept. 27 at the Solana Beach theater. Don’t miss it. Having seen a string of mindless, ho-hum new musicals, the critic approaches such a thing with grave foreboding. However, Salzman and Cunningham’s musical — despite a generic groaner of a title that makes sense only at the 11th hour — is smart, savvy and sexy. Cunningham’s book and lyrics, Salzman’s music and their development of character go far beyond surface scratching. All six performers are simply wonderful, and there’s a topnotch instrumental trio in the wings, headed by musical director/keyboardist Steven Withers. The others are percussionist/drummer Tom Versen and Matt Best on reeds. Add the witty costumes of Jennifer Brawn Gittings, the hair and wig design of Peter Herman, a facile, abstract set by Marty Burnett, lighting by Matt Novotny and choreography by Justin Deater and Krysten Hafso, and you’ve got a real winner. Matt Lescault-Wood, who’s proved himself invaluable of late, provides the sound design. The production is not perfect, but its flaws are fixable. The first act is too long. The second fairly zips along. The opening ensemble number, “Another Saturday Night in New York,” is overchoreographed (lots of arm flaps). The sound mix is problematic on the quartets. The characters are all self-involved young people intent on finding love/getting laid. The socially inept Austin (adorable, sweet-voiced Nick Gabriel) has just been dumped by his girlfriend of five years. A writer of greeting-card verse, he manages to say the gauche thing always. Austin’s polar-opposite brother, Jeff (Jason Maddy in his finest outing to date), operates in the physical world, peddling a pedicab and forever on the prowl, no commitments, thanks. He has a charming way of coming up with Malaprop phrases, like “getting all my ducks in line,” which everyone else is compelled to correct. Though they are also opposites, the two women are close friends. Diana (Kristen Mengelkoch) is an actuary and Marcy (Kelsey Venter) a fine arts photographer. Marcy, too, has been dumped, and in an opening scene the two devise a set of rules (“The Actuary Song”) to help Marcy find her true love. The result is a set of rules and timetables based on actuarial percentages, all of which promptly fly out the window once Marcy meets Austin and Diana meets Jeff. The two improbable relationships are hilarious and the outcomes are not too predictable; meanwhile, each character becomes dear and lovable to onlookers, as they say, “because…” All the world-wise waiters, baristas and bartenders — many of them un-PC — are played by adroit singer/comedians Geno Carr and Heather Anne Paton. Simas allows great, cringe-causing latitude here, and as the main characters jockey to score, the physicality of the sex scenes, especially Jeff and Diana’s, are also notably cringe-worthy on several levels. The enjoyment factor takes all, however, in this fine evening of music and manners. “I Love You Because” continues at 7 p.m. Wednesdays, 2 p.m. select Saturdays, 8 p.m. Thursdays through Saturdays, and at 2 and 7 p.m. Sundays, through Sept. 27. For tickets ($40-$44) and information, visit www.northcoastrep.org or call (858) 481-1055.