Ben Berry (MATTHEW McCONAUGHEY) is an advertising manager who wants to get away from hawking beer and sneaker products with his associates, Tony (ADAM GOLDBERG) and Thayer (THOMAS LENNON), and work on something a bit sexier, such as selling diamonds. Unfortunately, his boss, Phillip Warren (ROBERT KLEIN), has already given such a campaign to his coworkers, Judy Spears (MICHAEL MICHELE) and Judy Green (SHALOM HARLOW).
They're none too happy that he's trying to move in on their work, but agree to a bet to be judged by Phillip that will settle the matter. If Ben can get a woman they choose to fall in love with him and show up as his girlfriend at an event just ten days later, he can have the account.
They do so because during a visit to Composure Magazine's headquarters they overheard that "how to" columnist Andie Anderson (KATE HUDSON) is going to write an article about how to lose a guy in ten days by committing the same relationship-ending mistakes that many women accidentally or unknowingly make.
When they spot Andie and her friends, Michelle (KATHARYN HAHN) - the sad sack example behind the story idea - and Jeannie (ANNIE PARISSE), Spears and Judy pick her as Ben's target. Unaware of their insider information, Ben agrees and he and Andie then meet, positive that they'll have no problem pulling off their respective tasks. Soon, he's doing everything he can to make her fall for him, while she waits a bit before doing everything in her power to drive him away.
Yet, as Andie's boss, Lana Long (BEBE NEUWIRTH), puts pressure on her to finish the article in time for publication and Ben does what he can to act as if Andie's actions don't bother him, the two soon realize that they may be truly falling for each other. From that point on and as their respective deadlines approach, they have to figure out what to do.