YOU KNOW you're doing something right when you get the religious groups in America all wound up.

This is something Billy Bob Thornton achieved with interest last Christmas in the US with this depiction of the worst department store Santa ever.

And yes, Bad Santa is a somewhat controversial piece, thanks to its dirty mind and potty mouth.

A film for all those who find the Christmas period mawkish and overtly sentimental, it prefers to look at the underbelly of all that cheer, instead giving us a warts-and-all set of folk who use that time of year to take advantage of the rest of us.

Thornton plays the central anti-hero, and titular bad Santa, Willie, a role that both Jack Nicholson and Bill Murray turned down.

When we first meet him, to the beautifully tragic strains of Por Una Cabeza, he's getting completely blootered in a bar wearing his Santa suit, before staggering to an alleyway outside and vomiting beside some bins.

A man concerned with alcoholic rather than festive spirits, every Christmas he makes enough money to keep him in fags and booze for the year by robbing the department stores where he's working in tandem with his vertically-challenged partner-in-crime Marcus (Tony Cox), who poses as Santa's, literally, little helper.

But in the seventh year of their scheme, when Willie is heading for meltdown anyway, he comes across a crusty-nosed fat kid called Thurman (Brett Kelly) whose own tragic life causes Willie to reassess some aspects of his useless existence.

But if you're thinking already that this is some standard tale of redemption, think again, as it's more a case of him swearing less, as opposed to a complete reversal of his misanthropy.

It will be obvious for every audience member why Bad Santa, and its DVD release Badder Santa, have caused such a fuss Stateside. Not only is Willie a thief and a liar who swears like an Osbourne - and uses some choice vocabulary - but he also wets himself while sitting in the Santa seat and abuses the children to their faces.

He couldn't be any more of a moral vacuum, but it is exactly this which makes the film such a hilarious watch for those of a suitable age.

Director Terry Zwigoff, who made his name with the very quirky Ghost World, has managed to make a short and sadistic treat for the nasty nightmare inside all of us. And he gets a wonderful performance from Billy Bob, who makes it seem as if he doesn't really act at all, but is rather enjoying all the smoking, sex, language and drunkenness that the part demands he partake in.

But it's really Kelly's movie, his Cabbage Patch Kid features reflecting all of the small blackened heart the film possesses.

My advice? Embrace your inner sicko with this gem before the year's big Christmas warm 'n' fuzzy movie, The Polar Express, makes you actually retch.