Should you be shopping at the Tall and Fat store? Ask the owner, Thornton Melon (Rodney Dangerfield). "When you go jogging, do you leave potholes?" he asks in a TV commercial for the chain. "When you get a menu, do you say 'Okay'?" And away we go into an exercise in pure, hilarious, uncorruptibly corrupt Rodneyness.

Allegedly "Back to School" is a story about a father and son. Jason Melon (the lamentable Keith Gordon) doesn't like college much -- his grades are lousy, his only friend (cloying Robert Downey) has no friends himself, and he could only make the diving team as a towel boy. Dad wheels up in the limo to offer a pep talk, and ends up enrolling as a freshman.

The moments of emotion in "Back to School" ring phony, and the movie won't advance the cinematic art a whole lot. For the most part it follows the tired formula of the teen comedy, complete with bullying Aryan-style jocks who get their comeuppance, a snooty professor, a corrupt school administration and the usual rock 'n' roll, studying and brawl montages. Director Alan Metter has left the actors on their own -- if they're good, they're good, and if they're not, he doesn't help them any. And you could drive a truck through some of the cues.

But the screenplay is inventive (probably courtesy of Harold Ramis, who cowrote) and the cast includes some special actors, among them Ned Beatty, playing the smarmy hypocrite "Dean" Martin in high Eddie Albert style, M. Emmet Walsh as the goofy diving coach, Burt Young as Thornton's grizzled bodyguard and Sam Kinison, who ignites the screen in a cameo as a crazed Vietnam vet turned history teacher.

Besides, criticizing "Back to School" because you don't like the parts without Rodney is like criticizing the circus because you're bored by the fellow who sweeps up behind the elephant. You're there, simply and exclusively, to see Dangerfield, with his bulging eyes and brandy-snifter build, moving through the collegiate crowd with his greasy aplomb, whipping out a checkbook at the bookstore and bellowing, "Hey folks, it's on me -- Shakespeare for everyone!"

If "Back to School" is nothing more than a jury-rigged showcase for Dangerfield's stand-up routine, the result is nevertheless as funny as any movie this year. Awkward and twitchy, Dangerfield is something of a bully in behalf of his values -- cheap sex and expensive surroundings -- but he's also constantly, touchingly desperate to ingratiate himself. When he commences all that jiggling, it's almost as if he's trying to wriggle his way under your skin. And he does.

Back to School, opening today at area theaters, is rated PG-13 and contains profanity and sexual themes.