“Anger Management” delivers so many of the key elements of classic comedy that the movie’s nagging and altogether unnecessary flaws can make you, well, furious. Adam Sandler plays one of his trademark roles as a nebbishy nice guy locked in a frustrating and demeaning job (designing marketing on a line of sweaters for  overweight felines) but who nevertheless keeps company with a sweet and beautiful girlfriend (Marisa Tomei). In the course of a business trip, he sits down next to a bearded, wild-eyed eccentric (Jack Nicholson) and, with his nerves already frayed, goes through a painful misunderstanding with an arrogant flight attendant. This confrontation (memorably included in the movie’s widely screened trailer) leads to a courtroom where Sandler gets sentenced to a hefty fine and the completion of a required course in anger management. When he arrives at the mandatory group therapy session he not only meets an odd assemblage of explosive weirdos (including John Turturro, Luis Guzman, and January Jones and Krista Allen as a pair of lesbian porno stars) but discovers, to his horror, that the psychologist in charge of the program is Nicholson — the same weirdo who aggravated him as his seat-mate on the ill-fated flight.

The clever screenplay shows the anger management training making Sandler more and more enraged, leading to further trouble with the law and ever deeper entanglement with Nicholson’s odd-ball expert — a deliciously diabolical character who puts the psycho back in psychologist. As part of the court-mandated training (and an alternative to hard time in jail), Nicholson forces our anti-hero to confront a one-time bully from his past (John C. Reilly), to pick up a transvestite prostitute (Woody Harrelson), and to make an embarrassing pass at a beautiful stranger (Heather Graham) at a bar. The members of the starry supporting cast clearly enjoy themselves, catching the infectious energy Nicholson brings to his role. Sandler expresses the same barely repressed fury, hidden beneath a timid, long-suffering exterior, that earned him such excessive praise for his “serious” role in “Punch Drunk Love.” The last straw for his sad-sack character comes when his wacky therapist begins making moves on his lovely and sensitive girlfriend (Tomei), conspiring to break up her relationship with Sandler in the process.

Nicholson is so ferociously good as a crazed but inspired psychobabbling guru that he makes his juicy characterization the only believable aspect of the movie. The rest of the personalities and relationships look like convenient cartoons rather than people – especially the inexplicable connection between Tomei (who’s supposed to be a brilliant teacher of poetry) and her dim-witted loser of a boyfriend, who doesn’t know the difference between Emily and Angie Dickinson.

The often entertaining movie also suffers from an insistent and unfunny smuttiness – with more than a dozen very graphic references to male sex organs, with embarrassing comments about their gargantuan or diminutive size. Allen Covert plays a major supporting role (as Marisa Tomei’s best pal and would-be lover from their student days at Brown University) whose purportedly enormous endowment inspires detailed discussion in virtually every scene in which he appears.

An expertly staged climactic scene (with a clever if implausible twist) more or less redeems the movie; it’s difficult to resist Rudy Giuliani, his fiancé Judy Nathan, Roger Clemens and Derek Jeter working together in flattering cameos. There’s even a bit of intriguing substance rattling around in the midst of the contrived comedy, with a savvy message about aggressively insisting on daily respect (rather than quietly suffering petty indignities) as the best means for avoiding explosive anger.

In that spirit, it’s time for the movie-going audience to get more aggressive in its insistence that the Motion Picture Producers Association show more respect for its own increasingly absurd ratings system. The PG-13 rating for “Anger Management” is, quite simply, an outrage. The kinky sexual material (including repeated references to threesomes and passionate mutilation and fellatio and prostitution and transvestitism, along with a striptease to bra and panties by Heather Graham) make this movie wildly inappropriate for most fourteen years olds, let alone the nine and ten year olds who regularly flock to PG-13 material. The R-rating would have provided an appropriate warning for parents who might sanction such material for their kids, or for other adults who personally savor such raunchy comedy, but the current designation constitutes an egregious example of misleading labeling.

THREE STARS for the skillful, entertaining, though annoyingly flawed “Anger Management."