A more fitting title would have been Bad Movie.

Easily the lamest film I’ve seen this year (and I’ve seen Green Lantern), the latest from Walk Hard director Jake Kasdan promises a female-driven take on the politically incorrect classic Bad Santa and spends 92 minutes breaking that promise. The problem isn’t that Bad Teacher is never quite as funny. The problem is that it’s never funny at all.

Cameron Diaz is completely miscast in the title role. Elizabeth Halsey is a seventh-grade teacher in an Illinois suburb who doesn’t even pretend to care about providing her students with a decent education. A running gag has her playing DVDs of inspirational classroom sagas such as Stand and Deliver and Dangerous Minds while she nips at a bottle, naps at her desk and dreams up ways to pay for a boob job.

Which she needs for one reason: to snag the nerdy new substitute teacher, Scott Delacorte (Justin Timberlake), who happens to be the heir to a watch-making fortune. Hmm, a gold-digging, pill-popping bombshell with no sign of brain activity and a good-looking young millionaire. Sure, people like this answer the siren song of public education every day.

That’s one of the many problems with the uninspired, slapdash script by Gene Stupnitsky and Lee Eisenberg. It’s not rooted in any kind of credible reality. The creators of Bad Santa went to great lengths to fill in the details of Billy Bob Thornton’s background and to place him in a context that was plausible for his particular character. The characters in Bad Teacher have no such backstories and no such context. They’re just one-dimensional jokes who occupy a universe halfway between a “Saturday Night Live” skit and a cartoon.

Two of the other one-dimensional jokes are played by the British-born Lucy Punch and Jason Segel. She’s a goody-two-shoes rival for Timberlake’s affections. He’s a stoner gym teacher who’s smoked so much weed he honestly believes Diaz has a sweet, good-hearted side just waiting to be drawn out. That’s another of the script’s big problems: A blind 15-to-24-year-old can see where all this naughtiness is headed.

It’s disappointing enough — given the picture’s premise — that things never get much more outrageous than a little raunchy language and some cringe-inducing dry humping. The last thing you want from a movie like this is even a trace of by-the-numbers Hollywood redemption. Kasdan is so off his game here he can’t even cover up the fact that the final act is a patchwork of focus-group fixes. Watch for Diaz’s stand-in at the very end. Shot from behind, she’s easily a head shorter than the star.

Though who can blame the actress for getting as far away from this train wreck as possible and staying there? Certainly not anyone who’s had the misfortune to sit through it. If there’s a lesson within a mile of this mess, it’s that you’d be wise to stay away, too.