The new Nick Cannon comedy, ''Underclassman," is rated PG-13, but that puts an awfully large slice of America at risk of actually seeing the thing. Let me float the suggestion that it be rated PG-13-only, since anyone older than that will quickly realize he or she has better things to do than attend this pitiful ''Beverly Hills Cop" retread.
''Underclassman" is saved from total puff only by the obnoxiousness of its star, who seems to be laboring under the delusion that he's the next Eddie Murphy. He is -- how to put this kindly? -- not even a third-string Wayans brother. As Tracy Stokes, a Venice Beach bicycle cop who aches to prove he can bring down the bad guys, Cannon (''Drumline") preens and wisecracks with a maximum of sass and nothing that remotely resembles charm. In LAPD parlance, the kid has no backup.
But there's trouble at Westbury High: A reporter for the student newspaper has been murdered, and a young detective is needed to go undercover. The dropout son of a legendary cop, Tracy pleads his case to Lieutenant Delgado (Cheech Marin, looking in vain for an off-screen bong to ease the pain) and is soon the new kid in the halls.
Westbury High is one of those typical private schools where all the kids drive high-end cars and speak impeccable rap; the principal is a poncy Brit, and the impossibly hot Spanish teacher, Ms. Lopez (Roselyn Sanchez), wears belly shirts to class. Tracy decides to fit in by acting as outrageously as possible, and we're invited to take this as solid if overenthusiastic police tactics.
Befriending poor little rich kid Rob (played with exactly one facial expression by Shawn Ashmore, an actor who looks intriguingly like an adolescent George W. Bush), Tracy uncovers a carjacking ring, romances Ms. Lopez (''you're the most gangsta teacher I ever had"), and continually howls in delight at his own lack of wit. The film matches him stride for stride, reaching its nadir when a fellow cop is stuck in a bush ''dropping a deuce" while the bad guys get away in a Corvette. Not to worry, Tracy can catch up to them -- on foot.
Cobbled together from the body parts of a hundred better movies, ''Underclassman" ends with the hero temporarily kicked off the force but still managing to save his Spanish teacher from the clutches of the surprise villain (hint: he has a British accent). By this point, even reasonably sentient teenagers in the audience will have bailed and sneaked into ''The 40-Year-Old Virgin" in the next theater. Or ''Valiant." Or Ingmar Bergman's ''Saraband." Anything.
Another cinematic lemon orphaned by the Miramax breakup, ''Underclassman" has been sitting on the shelf so long that it's opening the same day as director Marcos Siega's next movie, ''Pretty Persuasion," a comparatively ambitious black-comedy attempt to court the ''Heathers" crowd. The earlier movie is thus like a dorky high school photo that some prankster has pinned to the front door of a college dorm -- Siega must be looking at it and blushing with chagrin. If he's not, he sure as hell should be.
Ty Burr can be reached at tburr@globe.com.