One of the early trailers for The Girl with the Dragon Tattoo, the David Fincher adaptation of history’s most successful Swedish potboiler, promised “the feel-bad movie of the year.” It was a good line, but it wasn’t truth in advertising. Despite its long parade of rapes, assaults, and serial murders, The Dragon Tattoo in all its iterations (the Stieg Larsson novel, the Swedish film, and now Fincher’s version) is fundamentally a conventional revenge fantasy: Dirty Harry for nerdy Marxists, you might say, in which a left-wing journalist and the leather-clad lesbian computer whiz who sleeps with him mete out long-overdue justice to rich woman-hating Nazis. Despite its lurid material and exotic locales, it actually boasts one of the more predictable story arcs of Hollywood’s holiday season — and indeed, of any project that the prickly Fincher has undertaken.

To find the real feel-bad movie of the year, you’ll have to turn to a less eccentric but equally talented director: Jason Reitman (the son of the comedy impresario Ivan Reitman), whose oeuvre — Thank You for Smoking, Juno, and 2009’s Up in the Air — has quietly established him as one of the sharpest observers of the contemporary American scene. His latest film, Young Adult, re-teams him with the Juno screenwriter Diablo Cody, and it pushes past the tragicomedy of his earlier movies into far darker terrain. Sold as a black comedy in the Bad Santa/Bad Teacher vein, Young Adult is really a tragedy disguised with laugh lines, which turns the clichés of high-school dramas and adult rom-coms to bleak and entirely unsentimental ends.

Reitman’s protagonist is Mavis Gary (Charlize Theron), a former high-school queen bee — gorgeous, leggy, and self-centered — who’s grown up to be the superficially successful ghostwriter of a series of popular Gossip Girl–style young-adult novels. Her career pays for a large, arid, and unkempt apartment in a Minneapolis high-rise, a Mini Cooper, and the kind of yappy little dog that every reality-TV starlet seems to covet — which isn’t a surprise, since Mavis’s flat-screen is constantly blaring the troubles of Real Housewives, Bachelorettes, and Kardashians.

It takes a birth announcement from her high-school beau (Patrick Wilson) to jolt her out of this endless feedback loop of narcissism, and into a feedback loop of self-delusion instead. After eyeing the baby picture for a while, Mavis decides to head back to her hometown of Mercury, pretending that she has real-estate business to conduct in order to buy time to seduce her ex-boyfriend away from domesticity and back into her bed. What follows is an escalating series of uncomfortable come-ons, in which Mavis proves that you can’t go back to high school, even as her sense of entitlement plumbs ever-more-horrifying depths.

In a more conventional movie, there would be a grand small-town comeuppance awaiting the former queen bee, which would leave her both personally humbled and morally improved. Young Adult supplies comeuppances in abundance, and it even provides a romantic alternative to Mavis’s married ex, in the form of Patton Oswalt’s Matt, a limping comic-book geek whose locker was next to hers but whom she remembers only because of the vicious, life-altering beating he endured at the hands of a gang of cruel jocks.

But as the movie proceeds, we realize that Mavis isn’t just a spoiled princess in need of a reality check, or a superficially “unlikeable” heroine who’s really decent way down underneath. She’s a deeply damaged person, less deplorable than pitiable, with no easy happy ending awaiting her — in Mercury, or anywhere on Planet Earth. Young Adult isn’t interested in teaching the self-absorbed prom queen a few lessons in humility. It’s up to something harder and more interesting: portraying the prom queen as a damaged, defeated, tragic figure, a former victimizer who’s become her own most tortured victim.

This portrait doesn’t quite add up to a consistent whole, because Reitman and Cody never quite decide where to lay the stresses. Sometimes they seem to be simply portraying a beautiful narcissist whose pathologies have hardened disastrously with age. Sometimes they seem to be making a movie about the wages of alcoholism, since most of Mavis’s disastrous behavior is floated on a tide of liquid courage. (Oswalt’s Matt becomes her confidant in part because he distills his own spirits and happily supplies her with them.) Then near the end, the filmmakers suddenly supply their protagonist with a tragic secret that makes her psychological profile seem almost too pat, and her behavior in Mercury too predictable.

But even when they’ve over-egged the pudding, Theron’s performance manages to hold it all together. Young Adult is not a pleasant movie, to put it mildly, and it isn’t an entirely successful one. It’s worth seeing, though, for the fearlessly plausible way that its lovely star inhabits a frequently repellent character, finding both moral abysses and raw humanity in one of popular culture’s great clichés. This isn’t a movie that makes you root for the bad girl. But once you’ve seen it, you’ll never feel quite so comfortable rooting against her again.