Fueled on booze and KFC, Mavis Gary - the unhappy soul played with scary conviction by Charlize Theron in Young Adult - is not someone you'd want to encounter before noon. She's probably not someone you'd want to encounter after noon, either, although she can put on a good face if you give her time with her makeup kit and a couple of shots of Maker's Mark.

There's certainly intelligence and wit there - albeit caustic, ruthless - and she was the high school prom queen, after all. But there she is, rolling out of bed at the crack of 10 a.m., shoving her little fluffy Pomeranian onto the balcony because she's too groggy to get dressed and take it for a walk. It's quite a picture.

And Young Adult, directed by Jason Reitman from a script by his Juno collaborator Diablo Cody, is quite a picture, too. (For a while, anyway.) A pitch-black comedy steeped in bitterness and regret, the film follows Mavis - single, cynical - as she gets the news that her old high school beau is now a proud dad.

This is back in little Mercury, Minn., and so Mavis, who lives in a high-rise in booming Minneapolis, climbs into her Mini Cooper, punches in an old mix tape, and drives back to her hometown to steal Buddy Slade (Patrick Wilson) from his loving wife and newborn. She may as well have a personalized license plate: HOMEWRECKER. Or, if that's too long, simply WRECK will do.

Theron is thrillingly nasty as Mavis. Her loneliness and desperation manifests itself in the contempt she shows for her old town and its denizens, in her self-destructiveness and serial consumption of liquor. It's a great performance, and Reitman - who went from Juno to Up in the Air, another deft character study of a flawed and somewhat self-deluded individual - lets her have the run of things.

But Young Adult, which takes its title from the genre of fiction Mavis ghostwrites (Waverly Prep, a series for tween girls), isn't as artfully realized as Up in the Air. Cody's screenplay falls apart just when it needs to be the most taut and true: during a painfully awkward confrontation on the front lawn of Buddy's house. And Wilson's character is a blank slate - he's impossible to read, perhaps because there's not much there, or because he's an idealized figment of Mavis' memory. But, still, he doesn't feel lived-in, real.

Patton Oswalt, the comedian who did a fine, dark turn in the 2009 indie Big Fan, brings more substance to his portrayal of Matt Freehauf, a nerd who was locker neighbors with Mavis in high school, who lusted after her, unrequitedly - and, as it turns out, unremembered. But when Mavis pulls up a stool at a Mercury saloon, Matt is right there, and they start to talk. "You're the hate crime guy!" she says, finally recognizing him. Matt had been brutally attacked in the woods behind the football field, pummeled by members of the football squad who thought he was gay.

The relationship that develops between Mavis and Matt during her brief and disastrous trip home has a sad-sack poignancy about it. They're a couple of losers. They're pickled in alcohol. They bond.EndText