There has been a slew of mainstream comedies this year centring around deliberately objectionable main characters who border on the sociopathic. Just last month we had Horrible Bosses, and while audiences were not supposed to sympathise with the titular torturers, their casually homicidal employees were presented very much as the film’s heroes. The entire cast of The Hangover (and its odious sequel) constitutes a legitimate menace to society who struggle to stay within even the broadest boundaries of respectability, yet are again introduced as the characters to root for. In Bad Teacher, the new comedy from Jake Kasdan, it is Cameron Diaz’s selfish, lazy, disrespectful and largely incompetent Elizabeth Halsey who craves our attention and sympathy.

Desperate to secure a man who will give her financial security and let her leave the profession she so clearly despises, Elizabeth decides to get breast implants. In order to pay for the surgery she recruits her 7th grade class to help raise money with a car wash, as well as extorting cash from parents supposedly for tutoring and classroom supplies. When she learns of a cash bonus for the teacher whose class scores highest in the year-end exams, Elizabeth sets her sights on winning, any way she can.

Cameron Diaz fully embraces the role of hard-drinking, drug-taking man-eater and scores numerous big laughs from her flagrant disregard for school policy, teaching ethics or acceptable behaviour. During the in appropriately seductive car wash sequence in particular, Diaz is only too keen to show off how good she still looks (she turns 40 next year), which compounds Elizabeth’s frustration when substitute teacher Scott (Diaz’s real-life ex Justin Timberlake) chooses the mousey Miss Squirrel (Lucy Punch) over her, leaving only Jason Segel’s out-of-shape gym teacher as a viable option.

Where the film fails is in its inability to capitalize on its potentially challenging premise. We never learn much about the students, or why Elizabeth got into teaching rather than any other profession. Once or twice the script hints that she can give quality advice when she wants to, albeit slightly anarchic in its approach, but that story thread is never developed. Instead the film opts for a rivalry story, with Miss Squirrel becoming increasingly psychotic in her efforts to expose Elizabeth as a fraud. While Punch is great in the role, it always feels like the safe and easy option, and as such quickly becomes dull and predictable.

The result is a film that skims the surface of black humour just enough to draw us in without ever reveling in its potential for deviance. Bad Teacher is a decent role for Diaz, who could certainly use one after her nothing part in The Green Hornet and incessant screaming in Knight and Day, and the film may well prove to be a modest hit. However, those hoping for the subversive humour of Bad Santa, World’s Greatest Dad or Observe and Report will be disappointed as the overwhelming sentiment here is: Could do better.