Anyone familiar with Zwigoff’s two previous films, the remarkable and disturbing documentary Crumb and the screen adaptation of the graphic novel Ghost World, knows that Zwigoff understands the territory of outcast and depressed characters well. He doesn’t pull punches. He doesn’t make nice.

But if you don’t know Mr. Zwigoff’s work (and judging from the reaction of the audience I saw the film with, most people don’t) or you make movie choices based on television ads and not reviews, Bad Santa could be shocking.

Several people walked out of the show I saw. The audience seemed to be expecting more of a “Naughty Santa,” something playful and only mildly challenging to the relentless force-feeding of Christmas spirit that starts now well before Thanksgiving. Bad Santa is not that movie. Bad Santa does some nice skewering of materialism and other nonsense that drains some of the joy out of the holiday and makes even fairly cheerful people approach Christmas with ambivalence, dread or hostility.

Bad Santa is gleefully, consistently crusty and grimy. Until the end. Vomiting, urination, dripping noses and lots of drinking, sexing, smoking and swearing accompanies everything that happens in Bad Santa. And to prove emphatically that Willie T. doesn’t understand the true meaning of Christmas, he is constantly spitting out the Lord’s name in vain. He makes it sound really ugly, too.

I really felt for one family that left, parents and two pre-driver’s license teens. I’m only guessing, but I had the bad feeling that the kids talked Mom and Dad into going to the movie. Boy, are they sorry. They’ll never get to choose the movie again. Mom looked like she was ready to explode. The kids looked like they might never recover from having to sit through even half an hour of something so racy with their parents.

“There’s an adult world and a child’s world,” Willie T. gets told by his boss after he gets caught in a dressing room with a customer making loud noises. Bad Santa is for adults only, though much of the humor is charitably described as adolescent. There is no enjoying Bad Santa if you’re not ready to accept all that.

I did laugh often during Bad Santa, and there were some affecting moments. I’ve never seen an Advent calendar put to such comic and touching use. But when I wasn’t laughing I spent too much time grimacing at the muck.

Bad Santa opens with the camera panning from a snow-covered street into a festive holiday party in a bar. We see lots of happy folks sharing holiday cheer as Chopin plays (the music in Bad Santa is a high point). But the camera ends up at the end of the bar where Willlie T. is sitting in unbuttoned Santa suit, drinking shots and smoking up a storm. In voice-over he gives us his sorry history of being beaten by his father and generally living the opposite life of George Bailey.

Willie T. is a safecracker. He and his partner Marcus work only during the Christmas season. They get jobs as Santa and his elf - Marcus is a “little person” and African American - and case the store so that they can rob it on Christmas Eve. They have been doing this for years, and because the partnership is so profitable they stay together. Marcus is played by Tony Cox. His performance is sharp and acerbic. Marcus and Willie T. spar well. Marcus berates Willie, constantly trying to get him to shape up so he doesn’t screw up the job.

They are in Phoenix, a particularly absurd place to celebrate Christmas. Willie T. gets worse every year. He shows up drunk to talk to the kids. He swears at them and everyone else in the store. He cannot resist provoking anyone who gets in his way.

He meets his match when a chubby, nerdy kid starts following him. Willie T. treats the kid horribly, but the kid won’t give up on him. When the store security chief, a nearly wasted Bernie Mac, starts snooping around Willie’s hotel room, Willie moves in to the kid’s house. The kid lives in “nice digs,” a suburban McMansion with his grandmother, a nearly silent Cloris Leachman. The kid’s mother is dead. The kid’s father is going to be away for a long time “climbing mountains.” He’s actually serving time for embezzlement.

Willie also lucks out when he meets a bartender named Sue (Lauren Graham). She has a kinky attraction to Santa, and she sees something in Willie T.

Billy Bob Thornton has given two very funny performances this year: as the American president in Love Actually and as a good ol’ boy in Intolerable Cruelty. Though his performance in Bad Santa can’t be faulted, I enjoyed his shorter, smaller roles in those others films. They are just better movies.

John Ritter, in his last screen performance, gives a great, funny, deadpan performance as the nervous, strait-laced boss, Bob Chipeska. Even when he pronounces his character’s name, adjusts his glasses or twitches a bit, he’s funny. Bad Santa is dedicated to John Ritter, and though I’m sure the folks that made the movie mean it as a tribute, Ritter deserves better. From “The Waltons” to Bad Santa. Yikes.

Watching Bad Santa, I couldn’t help thinking of Sling Blade, a film that also features Ritter and Thornton. Ritter plays a lovely human being in Sling Blade. Thornton wrote, directed and starred in that difficult, fascinating film that won him an Oscar for Best Adapted Screenplay. you want to see Ritter and Thornton share the screen, rent Sling Blade.

And here’s another Willie T. moment of grumpiness. Bad Santa wasn’t helped by the fact that the movie started after 12 minutes of commercials and previews. Usually, I love previews, but the previews for a movie stuck in Bad Santa territory make you doubt the future of film. And the commercials are worse. There were six of them. I really resent having to watch commercials when I’ve already paid money for the movie, especially when the admission price has been raised recently. I hated the ad for the moronic video game, but I especially resent being scolded by an anti-drug public service announcement. We shouldn’t have to be “scared straight” when we’ve come out to be entertained.