Unless it involves banging a stranger in an airplane bathroom, Victor Mancini is not a stand-up guy. The main character of Choke is a sex addict who’s sorta-kinda working on his recovery while not even thinking about putting the brakes on his signature scam: going to fancy restaurants and pretending to have Hoovered down some windpipe blockage so a wealthy patron might save him and feel compelled to send the poor sap a buck or 20 every now and then. Victor steals from the rich, he tells people, in order to keep his mother, who’s suffering from dementia, in a private hospital. You get the feeling he’d do it regardless.

But this being a Chuck Palahniuk story, Victor (Sam Rockwell) is not his peccadilloes, just like Palahniuk’s Fight Club characters were not their khakis. That’s the (loose) moral of writer-director Clark Gregg’s adaptation of Choke: Others may label you an addict, con artist, or all-around jerk, but it’s what you decide you are that defines you—and it serves as redemption in a film with situations so seedy and humor so dark you’ll feel a little ashamed after laughing. Like when Victor finally tells a confused, dogged elderly patient at his mother’s hospital that, yes, he is the brother who molested her. “Absolutely, I boned you silly,” he says. The woman starts to cry; Victor tries to get through the door she’s blocking. “Listen, I’m sorry I hurt your woo-woo,” he says impatiently. “But it was like 80 years ago!”

Gregg, a first-time director best known for being one of David Mamet’s go-to actors, rarely lets the comedy slide toward wackiness and erase the story’s bleak undercurrent. Rockwell’s twinkle-eyed charm and Palahniuk’s gift for deadpan absurdity are crucial, however, to keeping Victor amusing, if just short of likable. He’s introduced at a sexaholics meeting, which he attends mainly to get laid, not to control his compulsion. He pictures every woman he sees, from nurses to nuns, topless. (A lot of the images turn out to be memories.) And his best friend is Denny (Brad William Henke), a chronic masturbator who works with Victor at a colonial theme park. Mostly, they just get in trouble there, irritating their boss (Gregg, in a funny bit part) to the point where even he forgets about the rules to constantly speak in “oldenspiel.” (If you think listening to people bitch about work is entertaining, try hearing it in colonial English.)

Choke’s plot is essentially about Victor’s inability to tackle the fourth of an addiction program’s 12 steps: taking inventory of one’s messy life in order to move on. While Denny falls in love—to a stripper Victor relentlessly denigrates, one of his truly jackass habits—Victor finds himself unable to turn Dr. Paige Marshall (No Country for Old Men’s Kelly Macdonald) into a notch on his pillory. He blames the chapel she always wants to do it in (“I’d like to see you cop a chubby with the Holy Savior staring down your crack,” he tells Denny), but it turns out Victor actually has feelings for her and has yet to regard like and lust as anything but mutually exclusive.

The person who really begins to tear down Victor’s lifelong defenses, however, is the one responsible for planting them—his mother, Ida (Anjelica Huston, radiant both in the fully-gray present as well as her black-haired flashbacks), whose condition is worsening and frequently speaks negatively about her son directly to him, believing he’s someone else. We learn that Ida was a con artist herself, never letting Victor do anything as pedestrian as run around a playground when they could steal a bus, and the boy was often placed in foster homes. Ida’s sudden desire to tell Victor the truth about his absentee father is developed into a rather funny, but nonetheless metaphorically meaningful, subplot involving that Holy Savior in front of whom Victor can’t get it up; this revelation, along with another twist, adds end-chapter layers to the film you never see coming at its Superbad-for-grownups start. Choke is not its dirty jokes, but another black-edged frame through which Palahniuk examines a life.