While Smith has matured to some degree as a storyteller, there is no escaping his undiminished fondness for raunchy, juvenile humor, which he indulges as liberally as one might expect in Zack and Miri Make a Porno. Whether he’s splattering his characters with bodily waste or poking gentle fun at their tentative exhibitionism, he pushes the envelope so often it’s as though he’s daring us to take offense. It’s mostly a front, though. Zack and Miri is Smith’s most tenderly romantic venture since 1997’s Chasing Amy and not quite the hardcore romp its title suggests.

The story unfolds simply, with few surprises. Zack (Seth Rogen, on loan from Judd Apatow) is a paunchy, good-natured lay-about who spends his days whipping up lattes at a Starbucks knockoff. Miri (Elizabeth Banks, of W.) is his penniless roommate whose sole ambition is to seduce the star quarterback at her high-school reunion. Neither is particularly successful, a point driven home when their power and utilities are shut off in the midst of a harsh Pittsburgh winter.

Inspired by a former classmate who has made his name in the porn industry, Zack and Miri decide to make a movie of their own. They begin with an eroticized reinvention of Star Wars, which remains one of Smith’s most exhaustively referenced obsessions. (“Star Whores” features the likes of R2-Teabag, Hung Solo and Darth Vibrator.) When their initial foray into the world of X-rated entertainment gets scrapped, Zack resumes shooting in the coffee shop where he works, something Smith, who shot Clerks in the convenience store where he was a cashier, would know about.

Smith loads the movie with visual gags and cringe-worthy physical comedy to match his gleefully vulgar dialogue, and his aim is often true. But what distinguishes Zack and Miri from his more pedestrian outings is a cast that gives his adolescent silliness a warm-hearted glow.

Craig Robinson, of TV’s The Office, is the heaviest hitter in a supporting cast that includes Jason Mewes (the talkative half of Jay and Silent Bob) and onetime porn star Traci Lords. It is Rogen and Banks, though, who take a pair of sweet, blue-collar kids and play them as endearing innocents even as they contemplate careers in the smut business. Zack and Miri are utterly without cynicism, and we root hard for them to succeed.

It comes as no surprise when Zack and Miri fall for one another – they’re a natural match, only too blinded by familiarity to notice. Smith keeps their courtship simple: Zack gets the girl, Zack loses the girl, Zack comes to his senses and (rather hastily) wins the girl back. It’s a classic love story dressed up as something a bit racier, and not only do we know where it’s going, we know just how it plans to get there. That’s okay, in the end, because Smith and his leads make Zack and Miri a couple worth knowing.