Cameron Diaz slips into super bitch mode in this daft but refreshingly amoral comedy from director Jake Kasdan (Orange Country, Walk Hard: The Dewey Cox Story) that takes the premise of Terry Zwigoff’s Bad Santa (2003), dilutes it and switches the setting from a shopping mall to a classroom.

Elizabeth Halsey (Cameron Diaz) is the titular poor role model protag whose driving motivation throughout the narrative is, well, her tits.

Halsey wants to invest in a new supple fulsome rack, but, divorced by her rich opera loving hubby, needs to find a way to raise the cash. She learns of a bonus teachers receive for excellent student study scores, and switches from a who-gives-a-shit? seat warmer to a classroom Nazi before realising she can simply cheat.

Amy Squirrel (Lucy Punch) is Hasley’s do-gooder colleague who cottons on to her wicked ways; Justin Timberlake plays a dry humping super dork and Jason Segel, so good at Hollywood’s always approachable everyman, is the PE teacher hoping to one day get into her pants.

The underlining joke is that Diaz is an incongruous whatev-goes teacher who cares more about her lipstick than her students’ welfare. She drinks, smokes and eats fatty foods, the means through which Kasdan reminds us she is bad, mmmay? But sadly the film shows her bad habits  halfheartedly: a quick shot of Diaz holding a chunkalicious burger, a flicker of her with a cigarette in her mouth, a snifter of a drink here or there.

Compare this ho-hom version of horribleness with the brilliant slobbering train wreck of Billy Bobs performance as a perpetually pissed Farter Christmas in Bad Santa and you’ll quickly realise how many opportunities have been missed, how pale this riff on the same tune is by comparison.

Diaz is sexy with a slight snarl. For her character to really resonate in the way she was intended — as a who-can-tame-her-Devil-in-Prada-mean-mother-fucker — she needed to have upped the ante, to sacrifice her sexiness for a moment by, say, having her wake up, post hells bells bender, in a pool of vomit. The reason we can’t imagine her character doing this is the key to why the film falls down, why it only ever resonates in half measures.

And yet plenty of the jokes work and the comedy has a bitchy frothiness that’s hard to pass up. It’s amusing to compare Timberlake’s lamingtons-n-tang character here to his drug sniffing party boy incarnation in The  Social Network; this is his way of demonstrating range. The transition isn’t entirely convincing — far from it — but given his aw-shucks role as a king by-the-numbers doofus in Bad Teacher is cushioned by wink-wink comedy it works. At least for the most part.

Bad Teacher’s Australian theatrical release date: July 21, 2011.