After a highly effective smutty wink of an ad campaign, one could be forgiven for thinking that the ''bad'' in Bad Teacher refers to a public-school educator who fools around with her students. A lot of adolescent males may turn out opening weekend in the hope of seeing Cameron Diaz stoke their hot-for-teacher fantasies. But that sorry, dudes! is not what the movie's about. Make no mistake: Diaz's Elizabeth Halsey is bad she's a heartless, coarsely self-centered, and manipulative schemer. The only reason she's a teacher at John Adams Middle School is because her fiancé dumped her for being a gold digger, and she needs to support herself. Her one goal in life is to land $10,000 for breast-enhancement surgery.
To get through the day, she babysits her seventh graders by showing teacher movies like Stand and Deliver; she smokes dope and lies through her overbright red lipstick; she makes racial slurs (''This is why the Japs are overtaking us!'' she exclaims, reading her students' papers); and she flirts like a paid escort with the sexy-nerd substitute Mr. Delacorte (Justin Timberlake) but only because he's the heir to a watch-company fortune. The basic joke of Bad Teacher, which director Jake Kasdan hits over and over again, is that Elizabeth is the most dislikable character of the year. Diaz, in smeary make-up, certainly makes her ill-tempered shrillness convincing, but there isn't much spark to her performance, and there's so little bounce or real shock to the film's overly controlled look how rude we're being! black comedy that the audience is left stranded. We're not on Elizabeth's side, or anyone else's, really. We're just watching a film try to pass off misanthropic blunt-wittedness as ''edge.''
Kasdan thinks in outdated music-video shorthand, trotting out Diaz in Daisy Dukes for a ''horny'' car-wash scene, and getting his actors to pelt each other with invective. Timberlake has enough campy sincerity to make you wish he'd been allowed a different note, and Jason Segel, as a romantic phys-ed instructor, lays on the puppy-dog sweetness. The one actor I enjoyed was Lucy Punch as Elizabeth's nice-teacher enemy. Bearing a physical resemblance to Lady Gaga (though more angelic and less outlandish), she turns this Goody Two-Shoes into the world's most self-actualized Valley Girl. Even when she's insufferable, you like her. That's a trick the movie could have used more of. C