Mean backstabbing humor that hits the funny bone. Young Adult, directed by the steady all-naturalistic hand of Jason Reitman (“Juno,” “Up in the Air”), has Charlize Theron in full bitch mode. As a Minneapolis author of teen novels, Theron’s Mavis Gary is superhot – but hardly beautiful because she is unhappy under the skin. Watching the amazingly combustible Theron in this flick has you recalling the prom queens or uber-socialites from your high school and wondering if they are idle and unfulfilled today. For Mavis, she has an objective to reclaim her happiness: She returns to her humble hometown roots to steal back the guy she was in love with from high school, the doofus but handsome straight-arrow Buddy (Patrick Wilson), regardless that he’s married with a newborn.

Co-star Patton Oswalt steals plenty of scenes as a middle-aged geek cripple. Back in high school, Matt Freehauf had a locker next to Mavis’ but was ignored. He became pitied for being the “Hate Crime Guy,” albeit he was the victim, not the perpetrator. Why does Mavis befriend Matt when she returns to her culturally flat hometown? Because she’s an alcoholic and Matt is a systematic drinker and full of bantering bar jibe. Is Matt in love with Mavis, too? It’s obvious: “Guys like me were meant to always be in love with girls like you.” But Mavis is a big girl so she knows how to keep a lowly chap in check.

Mavis is ingratiating to Buddy’s wife Beth (Elizabeth Reaser), all ready of course to pounce her husband the second she exits from the room. Mavis has been invited to the baby-naming ceremony. But she really just wants to steal Buddy away so they can get sloshed. In subsequent opportunities, Mavis spends her daily hours prepping with manicures, pedicures and facials, getting ready for her big night out with her ex. It’s horribly funny that their reunions take place at a ribs and beer joint where she is blatantly overdressed with her silicone backless bra sponging underneath her black cocktail dress.

While Julia Roberts tried to break up a wedding before it happens in “My Best Friend’s Wedding,” Mavis is busy trying to break up a consolidated one. She’s less like Julia and more like the Cameron Diaz tramp in the underrated “In Her Shoes.” Except that she does have a very spiky sense of humor and a tart way of dealing with situations. But she is a human lightning bolt: If she can’t have Buddy then she will unleash wrath unto everybody. Her words are as vindictively incisive as Sissy Spacek’s telekinesis powers in “Carrie,” she’s that much of a colossal of human destruction.

Mavis is a deluded lunatic – the repetitious Teenage Fanclub song motif insists on it – but writer Diablo Cody (“Juno”) makes her protagonist human enough. The film finds its pathos between Mavis and Matt ultimately. But the ending is more a tart than a whopper, and it’s not nearly as haunting as the finale of even the similarly themed “Little Children” which also had doofus-stud Patrick Wilson in an adultery situation. You might consider: All this real-life disgrace has led her to succeed in the cutthroat big city.

93 Minutes. Rated R.

BLACK COMEDY / MOODY CHARACTER DRAMA / WEEKEND DEBAUCHERY

Film Cousins: “Working Girl” (1988); “My Best Friend’s Wedding” (1997); “In Her Shoes” (2005); “Little Children” (2006).