Take director Kevin Smith—the genius behind “Clerks” and “Dogma,” who basically revolutionized teen angst flicks—and comedy beast Seth Rogen, throw in a bunch of real-life porn stars, add a handful of Smith’s old crew and Rogen’s posse, and you should get a masterpiece. But as “Zack and Miri Make a Porno” proves, this collaboration is only brilliant in theory. The mixture of these pop icons, each of whom has proven masterful on a singular level (yes, even the porn stars), is not only toxic, but pitiful. While isolated moments prove funny—mostly because they’re outrageous—the film is a total flop, a rare tapestry of hilarious individuals who flounder in the wake of inexcusably bad writing, a terrible plot, and unbearable clichés.

The setting is Monroeville, Pa., a typically gritty Smith-style suburb in which vulgarity seeps out of the gutters. Zack (Rogen) and Miri (Elizabeth Banks) are the archetypal faux-platonic best friends who met in the first grade—he probably stuck gum in her hair and they were hooked—and for whom extreme sexual tension causes many an awkward moment. They live together in a dingy apartment, where the only source of heat is an ignited trashcan that constantly crackles in the background. Zack works in the local coffee shop, a warmly lit hub run by an old Indian man who speaks as eloquently as his colleagues, telling Rogan and his associate Delaney (Craig Robinson), “I hate both of you ebony and ivory fuckers.”

The film begins with Zack and Miri’s 10-year high school reunion. This uncreative and unfulfilling premise—hello “Romy and Michelle’s High School Reunion”—proves as dull and hackneyed as expected. Miri makes a fool of herself by hitting on her high school crush, Bobby (Brandon Routh), who is clearly gayer than Richard Simmons. We meet Bobby’s gay porn-star boyfriend, Brandon (Justin Long), who recognizes Miri from a scandalous YouTube video in which a group of horny teens catches her dancing in granny panties. Of course, all this porn gets Zack thinking. “Let’s make a porno! Everybody wants to see anybody fuck!” he says to Miri. She agrees, hoping to pay the bills and finally sleep with her best friend, whom she not-so-secretly loves.

This time around, Smith’s motley crew is a group of pornographically inclined misfits recruited by Zack and Miri to translate their porno vision into reality. Traci Lords and Katie Morgan bring their experience in pornography to the film, compensating for Rogen and Bank’s dire lack of finesse. Lords plays Bubbles, whose talent for blowing bubbles out of her vagina may actually be the best thing in the film, while Morgan portrays Stacey, the porno version of Elle Woods—she even has a little Chihuahua. “Clerks” fans will be happy to see Jason Mewes as Lester, the heavily tattooed village idiot who knows an impressive amount of kinky jargon. Ricky Mabe, the little boy from the “Lassie” series, plays the innocent, blue-eyed Barry, whom Bubbles quickly straddles and corrupts. But an all-star cast does not necessarily make a good film.

After a failed first attempt at a porno, entitled “Star Whores,” the group quickly regroups and puts on “Swallow My Cockachino,” featuring “whorista” sex and espresso bean lathering, shot right in Zack’s coffee shop. Together, the bunch becomes the best of friends, paying each other’s utility bills and serving as Zack and Miri’s fairy godmothers. They nudge the romance along through its literal and emotional climaxes, which happen to be separated in the context of this film. Who knew porn stars could be so sensitive?

Zack hits the nail on the head when he tells the group his coffee-shop porno idea has “production value waiting to have balls on it.” The same could apply to “Zack and Miri.” In theory the premise is hilarious and fresh, requiring serious maneuvering to bypass an NC-17 rating. But beyond its shock value, “Zack and Miri” has no substance—that’s where Smith and Rogen fail. Moreover, the pornographic aspects of this film only undermine the comedy and prove annoyingly vulgar.

Smith and Rogen both fumble with the basics, suggesting a bad chemical reaction. The film is primarily underscored by what sounds like a bizarre combination of trance and elevator tunes. The writing is forced, clinging to generic jokes, such as the racist implications of asking a black employee to work on Black Friday. Rogen, known for his improvisational style, is apparently incapable of delivering lines naturally if they’re actually written in a script. Smith relies too heavily on what I like to call “WTF moments,” like when Stacey poops on the cameraman during a shoot or when Brandon, the gay porn star from the high school reunion, discusses his recent revelation that his boyfriend’s anus has become “a gorgeous orchid.”

If there’s one takeaway from this film, it’s that some things just shouldn’t go together. Kevin Smith should stick to convenience stores and apocalyptic storylines involving Alanis Morissette as God. Seth Rogen should continue writing and starring in his own films about pregnancy and potheads. And Hollywood and porn should go back to their own separate lives and stop fooling around with each other.