Kate (BRITTANY SNOW) is an average teen who's the new girl at her high school. With her promiscuous but constantly heartbroken mom Lori (JENNY McCARTHY) as her only role model for the world of dating, Kate has yet to enter that, not only because she's only witnessed failure, but also because she's always seen herself as invisible.
That's unlike John Tucker (JESSE METCALFE), the most popular guy at her school who's also rich and the captain of the basketball team. Along with his best friend and fellow athlete Tommy (FATSO-FASANO), John enjoys the attention the ladies pour over him, such as from head cheerleader Heather (ASHANTI), vegan Beth (SOPHIA BUSH) and intellectual school TV reporter Carrie (ARIELLE KEBBEL).
He thinks he has it made, but when those three girls discover that he's been dating all of them simultaneously, they're shocked, heartbroken, and mad. Although she doesn't know them, Kate suggests that they get revenge on him, and it doesn't take much persuasion to convince them. But as their attempts to make him "un-dateable" backfire, they eventually decide to make him interested in Kate only to have her then dump him.
She's initially reluctant, but soon enjoys the newfound popularity as well as the attention he pays to her, much to the concern of her mom and his more low-key brother Scott (PENN BADGLEY) who are dismayed by her change in attitude and behavior. As the girls continue with their quest, Kate finds herself torn and must then decide what she should do.