They say that the secret to great comedy is timing. Well that’s just humbug; the secret to great comedy is having material that makes people laugh. Bad Teacher is a film that is screaming out to be described as a black comedy, but ultimately ends up just being grey.

It’s the end of term and Elizabeth Halsey (Cameron Diaz) is just wrapping up after teaching in a school for a year. She’s moving on to bigger things; bigger and more expensive. She’s bagged herself a rich fiancé and looking forward to a life of luxury. Which is just as well as she sucks a s a teacher; if you had Dead Poets Society John Keating (Robin Williams) at one end of the teaching spectrum as the coolest teacher, Elizabeth would definitely be right at the tip of the other lower end.

Unfortunately for Liz, her dreams of living off of her hubby-to-be’s fortune are dashed when he dumps her. This leaves her with no other choice than to return to her teaching job to get by.

Her main method of teaching is sitting her kids in front of a TV and making them watch endless films set in schools. What she wants more than anything are breasts; newer bigger ones for herself which will undoubtedly make her more attractive to members of the opposite of sex who have a healthy bank balance.

But big boobs cost even bigger bucks to buy. So she uses as many underhanded methods within the school system to get her breasts fund pumped up.

At the same time, Liz is distracted by the arrival of Scott (Justin Timberlake), a new substitute teacher to school, who also happens to come from wealthy stock. Liz pulls out all the stops to snare him, but faces stiff opposition from super teacher Amy Squirrel (Lucy Punch). But no-one plays dirty quite like Liz.

Insert your own amusing line here.

So there you have it, Cameron Diaz starring in a film where its title says it all. But what the title rather conveniently forgets to imply is that the film isn’t very funny. Much like one of the students in the film itself, it tries incredibly hard to make an impression, but fails miserably. So who should get the ‘F’ grade? Undoubtedly the writers.

Here’s the biggest shock though, both Gene Stupnitsky and Lee Eisenberg have written numerous episodes of one of the most consistently funny sitcoms on US TV in recent years by way of The US Office. There film track record however is less impressive, as the pair co-wrote the awful Year One together. Add this to their joint film CV and it doesn’t bode well for Ghostbusters III which they’re supposedly currently in the process of writing.

Everything about it is lazy, predictable and lowest common denominator. The basic premise is just a rip-off of 2003’s Bad Santa with Billy Bob Thornton, but without the jingle bells. One of the scenes in the film sees Diaz seductively washing cars; it’s not a bad scene, but has been done before, most notably by Liv Tyler in 2001’s One Night at McCool’s If it’s not original, then it’s inclusion must therefore be for titillation purposes only.

Diaz does little wrong, considering the poor quality material that she has to work with, but it won’t end up being a highlight of her career.

After a great turn in The Social Network, Justin Timberlake is a disappointment though as the wishy washy sub. His performance feels like he’s doing a sketch on Saturday Night Live that doesn’t go down at all well. Maybe comedy just isn’t his thing.

The director Jake Kasdan should also take his share of the blame. If he wanted to push the film into blacker comedic waters, he should have paddled for his life. But he really lets himself, Diaz and the audience down by allowing Diaz’s character to have a heart by the film’s end. Guess what folks? That there bad teacher ain’t all bad after all. Now there’s a surprise.

Everyone involved in this film should be sent home with the words ‘must try harder’ ringing loudly in their ears.