Set in 1988, the film begins in a music store with recent MIT graduate Matt Franklin (Topher Grace), his twin sister Wendy (Anna Faris), and his best friend Barry Nathan (Dan Fogler) as they try to figure out when to see Matt's dream girl Tori Frederking (Teresa Palmer). Following graduation, Matt has been working at a Suncoast Video store at a local shopping mall while trying to figure out what to do with his life. While working one day, Tori randomly walks into the store. When she asks him where he works, he lies and tells her he's at Goldman Sachs. Tori then invites him to a Labor Day weekend party held by Wendy's boyfriend Kyle Masterson (Chris Pratt). Matt, Barry and Wendy drive to the party later that night, but before they arrive, Barry steals a car from the dealership from where he got fired earlier in the day for his bad sales record.
At the party, Kyle challenges people to ride the "ball," a hollow steel sphere that is supposed to ride down the street. Matt runs into Carlos (Demetri Martin), a high school classmate who actually works at Goldman Sachs. Barry tries the cocaine Matt found in the stolen car, and is involved in a dance battle, after which Kyle proposes to Wendy.
Matt and Barry leave the party with Tori and her friends to go to a business party in Beverly Hills. During the drive to the party, Tori tells Matt that her boss, Peter (Michael Ian Black) hired her just to see her naked. At the party, Tori reveals to Matt that she hates her job. Matt and Tori leave the party, enter the backyard of a neighbor's home, and jump on a trampoline where they play truth or dare. When they get too far, Matt ends up sleeping with her. Then, Matt tells Tori the truth about his job, causing Tori to become upset and leave.
During the drive back to Kyle's party, Barry tells Matt that he should have that one night of enjoyment. Barry snorts cocaine that was hidden in the glove compartment in the car they stole. He persuades Matt to do it despite driving the car. Matt gets distracted which ends up crashing the car. When they get pulled over by Matt's county sheriff father (Michael Biehn), he damages the car even more to say that Matt should be working for a better company to pay off all the damages. Mr. Franklin lets them off with a warning when they should have been in jail. He tells Matt to take a shot at anything in life.
Matt and Barry return to Kyle's party. Wendy, having earlier told Matt that she applied for graduate school in England at the University of Cambridge, and is scared to open the admissions decision letter. Kyle opens the letter for her, and tells her that she has been rejected.
Matt and Barry walk back to Kyle's party, where Matt tries to tell Tori he is sorry for lying to her, but Tori is unwilling to forgive him. Barry starts to talk to the goth girl he met at the party still high on coke. He tells her that he is going to ride the ball and after one party goer decides not to ride the ball, Matt raises his hand and volunteers to take his place. Barry tries to discourage Matt from riding the ball, even offering to ride it for him but Matt tells him to "fuck off". He climbs into the ball where his sister, Wendy, tells Kyle not to let him ride the ball. Kyle tells Wendy that the hill goes up and the ball is just to scare people because it will actually roll back towards the house. But as Kyle releases the ball it damages several cars and goes off the road, coming to rest in a neighbor's pool. Matt nearly drowns but gets out in time.
Afterwards, Matt tells Tori he wants her home phone number but if he is being too weird, he can leave her alone. Tori is impressed by Matt's boldness by deciding to ride the ball, and he ends up getting Tori's number. Wendy, who didn't want Matt to ride the ball, ends up breaking up with Kyle.
Kyle pleads with her to stay but Wendy tells him 'no'. Kyle sobs uncontrollably as Wendy leaves.
As morning comes, Matt gets the card with Tori's number, and Mr. Franklin finds Matt's Suncoast Video name tag in the pool where the ball stopped rolling.