Chris Brander (Reynolds), an obese high school student in a suburban community in New Jersey, is in love with his best friend, Jamie Palamino (Smart). In 1995, on the night of their high school graduation, Chris attends Jamie's graduation party, and confesses his feelings to her by writing them in her yearbook; when he tries to return her yearbook to her, however, it is swiped by Jamie's ex-boyfriend Tim (Ty Olsson) and he reads it aloud at the party. Chris is then publicly humiliated when she doesn't reciprocate his feelings, instead giving him a kiss on the cheek and saying she loves him like a brother. After Jamie yells at their classmates for making fun of him, Chris storms away humiliated from the party on his bicycle, vowing to leave town and become more successful than all of them.
Ten years later, Chris is handsome and successful with a thriving career as a record producer in Los Angeles and a reputation as a ferocious womanizer. Just before Christmas, his boss (Stephen Root) orders him to take up-and-coming pop singer Samantha James (Anna Faris) to Paris so that she will sign with their company. Chris goes reluctantly, as he has a history with the self-obsessed James. On the duo's "business" trip to Paris, Samantha sets her private jet on fire by neglecting to remove the aluminum foil from her microwave dinner. This necessitates an emergency landing in New Jersey, not far from Chris's hometown. He takes her to his mother's house for the night, causing him to face the humiliating high school years he left behind and his unresolved feelings for Jamie.
Stepping out to the local bar, Chris runs into some old friends, including Jamie, who is working her way through graduate school as a bartender. Thinking that he can finally get his high school love out of his system, Chris plans to woo and seduce Jamie. However, a number of unexpected problems and the growing realization that his friendship with Jamie actually did mean something to him keep getting in the way. He bonds with Jamie on several occasions. But Dusty Lee Dinkleman, an even nerdier kid in school has now become a successful musician, and plans to have sex with Jamie and publicly humiliate her like she did to him when she told him she didn't like him. Jamie and Dusty bond and eventually he turns her against Chris when Samantha destroys Jamie's family's Christmas decorations thinking that Chris was sleeping with Jamie behind her back (she thinks that she and Chris are in a relationship). Angry and disappointed with Jamie and her family, Chris returns to LA only to realize that Jamie is the one for him. He leaves for his hometown again, goes to Jamie's house, and declares his love for her. And the film ends with some neighborhood kids watching Jamie and Chris kiss and a little boy gives one of the girls a cookie he made for her and she says "Thanks, you're a good friend'" suggesting that he may go through the same experience.
(Source: WikiPedia. Bangs_McCoy)