For the past several years, word has been that when Ghostbusters III is finally made (i.e., when they pin Bill Murray down, since no one else involved is doing much of anything), they'll be shooting a supposedly wonderful screenplay by Gene Stupinsky and Lee Eisenberg, best known for their work on The Office. As the years pass and we see more of the duo's work, this news becomes more and more distressing. First came the fitfully amusing but mostly uninspired Year One; now we have Bad Teacher, which (like their earlier screenplay) basically comes up with one interesting idea, and expects it to carry the entire film. I am not filled with high hopes for their Ghostbusters script.

The film's good idea is pretty much right there in the title (whose resemblance to Bad Santa is surely not coincidental): Cameron Diaz plays Elizabeth Halsey, who is a truly terrible teacher. She spends most of her days nursing killer hangovers while showing DVDs ("I think that movies are the new books," she explains to her principal). She's brutally mean to her students (Her notes on their quizzes include "Stupid", "Jesus Christ," and "Are you fucking kidding me?"). She does the bare minimum--until she finds out that the teacher whose class gets the highest test scores gets a bonus big enough to pay for the boob job she's getting to impress school sub Scott Delacorte (Justin Timberlake), a rich do-gooder.

Some of this, don't get me wrong, is funny, and Diaz is admirably game. But a little of it goes a long way, and Stupinsky and Eisenberg's screenplay never aims higher than easy shocks--Oh look! She's getting high! She's playing heavy metal music in her fast car! She's smoking a cigarette! She's saying fuck! In the era of Mary Kay Letourneau, Elizabeth hardly qualifies as a bad teacher. Without any real comic energy or momentum (the direction, by the usually capable Jake Kasdan, is surprisingly lackadaisical), the picture feels too often like a receptacle for cheap, easy jokes (I'm looking at you, men's room diarrhea gag.)

Where the film works is around the edges. Most of the supporting characters are the broadest possible types, and few manage to find a way to make them play--particularly Justin Timberlake, who has proven that he can be funny on, say, Saturday Night Live, but doesn't give this character any more depth than a five-minute sketch character on that show (and sure as hell isn't provided with any). He has one entirely funny scene, singing a laughably maudlin "original song" at a gig with the "faculty band," but he's saddled with a one-joke character and doesn't do anything with it (therefore rendering the script's love triangle free of any interest or suspense).

However, Lucy Punch (so funny in Hot Fuzz and You Will Meet a Tall Dark Stranger) is terrific as the teaching staff's perky, can-do overachiever with a screw loose, and Phyllis Smith (from The Office) nails every single comic beat. But the picture's comic MVP is Jason Segal, as the gym teacher with a thing for Diaz. He's not exactly crafting a rich and original comic character here--this is basically Marshall Eriksen plugged into a summer comedy. But his slightly springy line readings and scruffy likability couldn't be more welcome.

Aside from those occasional respites, there's not much to recommend in Bad Teacher; we all know that humor is subjective, and my Groucho Marx is your Adam Sandler, but the fact of the matter is, most of the time, it's just not that funny. It certainly never manages to push its central conceit past the obviousness of its trailers or posters ("She doesn't give an 'F'"--get it?). It's a filmed idea, and that's about it.

Jason lives in New York. He holds an MA in Cultural Reporting and Criticism from NYU.