Theater manager, take heed. There will be moronic parents who, with young brood in tow, will seek sympathy refunds after walking out of Bad Santa, claiming “they just had no idea.”

Keep the spirit of the film’s main character and tell them they should know better and to cram it. If they can’t investigate a movie’s content before going, they get what they deserve.

Now, kids definitely shouldn’t see Bad Santa, with its rampant swearing, booze-soaked protagonist and odd bits of violence. Hopefully they’ll never wallow in a hellish existence a la Billy Bob Thornton’s character. But neither should they live in a hazardously sanitary bubble like the boy he befriends, pretending things like bullies, liquor, crime, selfishness, sex and murder don’t exist.

Created with a significantly smarter hand than its advertisements let on, Bad Santa tells an intriguing story of two characters at complete extremes.

At the bottom of the barrel, licking whatever he can find, is Willie (Thornton), a walking 24-hour liquor store. His mission is to berate, pass out and sleep around. His means to do so are playing a department store Santa before robbing the store blind and drinking himself nearly to that state until next year.

And then there’s … well, he’s in the credits as “The Kid,” and it’s best to leave it that way. His name is revealed, and young actor Brett Kelly’s reaction to Thornton’s questioning of it is one priceless moment of many.

A grossly overweight latchkey kid with a snotty nose and a vacant stare, The Kid is a poster child for playground torture. His naïve devotion to the notion of a Santa Claus is both sweet and a little frightening. Kelly’s performance is a stunning one, for reasons understandable only if you see it.

Willie and The Kid are fascinating, not in changing each other, but coming to more of an agreement that sort of helps them both out. Bad Santa isn’t so much against Christmas as it is against being so sunnily ignorant of people who are miserable losers of any age. There are elements of Kingpin and The Ref (themselves fine films) in Bad Santa, but by comparison, its pure bitterness makes those films look like a pack of SweeTARTS.

 It’s like an equally dark, but more slapstick look at the themes of director Terry Zwigoff’s Ghost World. It has a sideshow vibrancy to animate the usually raunchy, but usually riotous, goings-on.

There is an assortment of deficient supporting characters floating about, and, yes, convoluted murder and robbery stories, although only Tony Cox as Willie’s “elf” partner and the late John Ritter as a fussbudget manager connect.

Bernie Mac’s wide-eyed intensity is wasted as a department-store detective. The role requires the drier wit of Bill Murray or dynamic facial movement of Tracy Morgan. And the movie is funnier when it’s being cynical and pointed rather than just raunchy, namely in every scene involving Lauren Graham as a barmaid with a Santa fetish. 

Still, at the center of it is an absolutely fearless performance from Thornton, known for his lunatic-fringe characters, but nothing like this. Willie’s self-loathing is present in every scowl, limp, and eruption of anger Thornton shows.

In the ending of a more conventional and condescending film, Thornton would dry out, get the girl and open a business. The kid would make friends of the bullies, get his father back and become King Cool in school. At its dysfunctional, hysterical conclusion, Bad Santa takes the notion of “happy,” puts it on puree and then pours it out — sort of how like life usually is.