Tammy- a woman with the inverted Midas touch

Thereís no fool like an old fool. When Susan Sarandon appeared in Thelma & Louise in 1991 she pushed back the boundaries of the 'buddy buddy' genre by transferring the emphasis from men (where it had primarily resided before) to women. But now, 23 years on, she's tried to re-heat that particular souffle in a madcap romp and the ploy simply doesn't work.

For all the word, Tammy looks like Thelma and Grandma Louise. It's written and produced by Melissa McCarthy, who also plays the (title) role of Sarandon's granddaughter. The pair of them go on the road together to escape lives that are going horribly wrong for both of them, and hopefully to repair their own hitherto ropey relationship.

Sarandon is also an alcoholic. Though aged around 70 (they've made her look older than her real age by dyeing her hair grey) she behaves like a naughty teenager most of the time. Even so, such behaviour looks like Shirley Temple in comparison to that of Tammy herself, an overweight young woman who displays an unerring knack of destroying almost everything she touches – usually on purpose.

But behind it all, Tammy is a sweetie. She has a good heart. Within the film's skewed parameters, this is supposed to make it all acceptable.

Is it? I wasn't so sure. Or maybe I'm just getting too old (in an un-Susan Sarandon-like way).

Some of the scenes are hilarious, like the one where Tammy decides to hold up a hamburger joint to get some much-needed cash to bale Sarandon out of jail but even here I felt there was a nod to Woody Allen's Take the Money and Run.

There's a lot of adult content in the film: sexual references, a lesbian sub-theme and much swearing. And of course no film of this ilk would be complete without Kathy Bates turning up near the end – which she does – along with other 'usual suspects' like Dan Aykroyd and Sandra Oh. Such casting is about as imaginative as the film's central concept.

There have been many brilliant road movies featuring older people made in recent years, like About Schmidt and Nebraska. This one misses the mark by some margin, largely due to its many concessions to adolescent humour. It would have been better off exploring the bonding theme between grandmother and granddaughter more, instead of souping up Tammy's 'car crash' life ad nauseam.

Within the first 10 minutes sheís lost her job and her husband and knocked down a deer. This gives us some inkling of the mayhem to follow. The film pretends to like old people but in actual fact it patronises them. Neither is there anything 'funny' about alcoholism, as Ms Sarandon would have us believe. And what's the great Toni Collette doing in a farcical cameo role?