Our protagonist is Mavis Gary (Charlize Theron), a thirty-something woman who was the prettiest and most popular girl in high school and never really got over it. (She still looks pretty good but it’s a lot more work now.) She long ago escaped from her stifling small town origins, moved to the big city and made a moderately successful career writing a series of Young Adult novels featuring impossibly popular high school girls.
But something seems missing in her life. The last straw comes when she learns that her old boyfriend Buddy Slade (Patrick Wilson) has just had a new baby. Suddenly she decides that she and Buddy were always meant to be together. So she packs up some clothes, stuffs her little dog into a duffel bag and heads back to her old home town, determined to win him back.
There she encounters a number of people she knew in high school, notably Matt Freehauf (Patton Oswalt), a chubby gimpy fellow who once worshiped her from afar (or rather, from the locker next to hers.) She doesn’t know who he is until she recognizes him as “Matt the Hate Crime Guy.” (In their senior year he was beaten and left for dead by some jocks who thought he was gay. He was quite famous for a few days until the media realized that he wasn’t gay, just overweight, and therefore the beating was nothing to be concerned about.)
For some reason she confides in Matt, and he immediately recognizes that her plan to break up Buddy’s marriage is deranged. Nevertheless Mavis and Matt keep running into each other and gradually form a bond. In some strange way they are kindred spirits. (This is not necessarily a good thing since his hobby is distilling bourbon and she is pretty obviously an alcoholic.)
Young Adult is one of many Hollywood movies that suggest that the kids who are super-popular in high school grow up to be middle-aged losers. This probably resonates with audiences that are mostly made up of people who were not super-popular in high school, but I don’t think it is generally true. The popular kids tend to have a talent for marketing themselves. They often grow up to be successful politicians, or the kind of CEO who retires with a $250 million severance package after running his company into the ground.