With so much talent in front of the camera (besides Cameron Diaz in the title role, the movie is also packed with experienced scene-stealers like Lucy Punch, Jason Segel, John Michael Higgins and Eric Stonestreet) as well as behind it (Walk Hard's Jake Kasdan directs and longtime scribes of The Office Gene Stupnitsky and Lee Eisenberg penned the screenplay) it's frustrating that so few of the first act jokes land. Instead of a movie, Bad Teacher starts off as a series of blackout sketches designed to highlight just how bad of a teacher Elizabeth Halsey (Diaz) is meant to be. And she's plenty bad. Liz's list of vices includes toking up in the car outside school, stealing the funds from a charity car wash and showing her pupils an endless stream of movies -- from Stand and Deliver to Dangerous Minds to Scream -- while she sneaks swigs from mini-bottles of Jack Daniels hidden in her desk. Her two major life goals aren't any more admirable. They are: 1) Marry a rich guy and 2) Raise the cash to pay for the boob job that will attract said rich guy. Elizabeth's unrepentantly nasty attitude is initially funny, but just as quickly turns tedious, partly because none of the characters around her seem to know how to react when she says something that's so flagrantly outside the realm of good taste. It's like she exists in a vacuum -- a soul-sucking, pitch-black, dream-destroying vacuum.

But just when the movie appears to pass the point of no return, a funny thing happens. I mean an actual funny thing, which is followed by another and then another. And before you know it, you're laughing hysterically when previously you were groaning and rolling your eyes. So what changed? Well, for starters, the writers finally hit upon an actual narrative to go along with their setting and main character. Granted, the narrative isn't exactly Game of Thrones in its complexity. Basically, after pissing away half the school year, Elizabeth suddenly turns into a super-teacher overnight, walking her class through the intricacies and subtle metaphors of To Kill a Mockingbird and even going off the syllabus to teach Animal Farm. She's not doing this because she cares about their education, mind you. Rather she's interested in earning the bonus that's awarded to the teacher whose class scores the highest on the annual statewide test -- a bonus that will finally allow her to afford those big honking new boobs she covets. What's so funny about Liz's transformation is that she doesn't really transform herself much at all. She's still rude to her students (her preferred way of teaching is to literally hammer the knowledge into them by chucking dodgeballs at their heads when they miss an answer) and puts herself before anyone else. The big difference is that she's being bad with a purpose and it's great fun to watch her manipulate the system to her advantage while refusing to change her personality one bit.

Once the writers put Elizabeth on this path, they allow the other characters to finally join the fray as potential roadblocks to her goal. Punch plays her primary nemesis, Amy Squirrel, an absurdly dedicated instructor that prides herself on her innovative teaching methods. Her dislike for Elizabeth soon turns into abject hatred, particularly as they both start competing for the attention of the handsome new substitute teacher Scott (Justin Timberlake, not quite as comedically comfortable here as he's been in his Saturday Night Live appearances. Maybe he's just weirded out about having to romance and -- at one point, dry hump -- his real-life ex.) Meanwhile, Segel's sarcastic gym teacher, Russell, represents a different kind of threat to our anti-heroine. He's poor, uncouth and loves small breasts, but he's also the one person in the entire school that isn't scared to match wits with her. To her shock, she finds herself digging him in return. Much like on How I Met Your Mother, Segel is Bad Teacher's secret weapon, one that the filmmakers maybe should have deployed more often. Whether loudly arguing with some seventh-grader about why LeBron will never surpass Michael or showing one of Elizabeth's students the best way to nail her with the dodgeball (his reward for getting an answer right), virtually every scene he's in is comedy gold.

The one element of Bad Teacher that's consistently strong throughout is Diaz's ferocious star turn. In many ways, this is the role she's been looking for her entire career. When she first appeared on the scene in the early '90s, she was typically cast as the sweet, innocent ingénue that dorky male comics competed for in movies like The Mask and There's Something About Mary, but one always got the sense that there was a bawdier comedienne inside waiting to burst out. While her initial attempts at darker, meaner movies (1998's Very Bad Things and 2002's The Sweetest Thing) fell flat, she finally gets the right role here and the film eventually rises to meet her. Because of its rough beginning and refusal to have its main character completely change her awful ways, Bad Teacher is unlikely to gather much in the way of awards attention for its star, but it still represents a high point in Diaz's filmography to date.

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