It's almost a Hollywood storytelling imperative: Make your main character likeable. Even if he or she starts off as the most loathsome of humans, be sure by the time the credits roll that your protagonist learns a lesson and reveals a more attractive personality.

Not so in "Bad Teacher," the June 24 comedy in which Cameron Diaz's couldn't-give-a-hoot educator — she routinely sleeps through class and lights up a joint afterward — remains largely unchanged. And it was the character's essentially static arc, Diaz told us recently, that attracted her to the movie, even if she initially thought she wanted nothing to do with it.

"The first 30 pages, I'm like, 'I am not playing this. There is no way I can play this character. There [are] no redeeming qualities to this character,' " she recalled of the script. "And by the end of it, I'm like, 'Oh my god, this is genius! There's no redeeming qualities to this character!' We got to the end of the script and we're not apologizing for anything she said. It's a very modest arc."

See, the teacher she plays, Elizabeth Halsey, begins the film with one goal in life: to put her bank account above love and marry a dude she honestly has no respect for but who can buy her a slick sports car without blinking an eye. Quickly, though, the guy ditches her, and she sets her mind to roping in a new rich boy, a substitute teacher played by Justin Timberlake.

A hefty heap of pot, some unscrupulous test-taking techniques and a whole lot of other bad behavior later, Halsey's plans pan out in a very unexpected manner. But by film's end, one thing remains hilariously the same: She's still kind of a crappy teacher.

"It's amazing that it exists in this movie because it is so rare," Diaz laughed. "I'm thrilled because it is so refreshing."

Check out everything we've got on "Bad Teacher."

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