| Director | Adam McKay |
|---|---|
| Budget | $65 million |
| Box office | $128 million |
Thirty-nine-year-old Brennan Huff and forty-year-old Dale Doback are immature adults who still live with their respective single parents. Brennan's divorced mother, Nancy, meets Dale's widowed father, Robert, and they marry, forcing Brennan and Dale to grudgingly live together as stepbrothers. Since Dale refuses to give up his office drum set, they are forced to share a bedroom. Despite Dale's warnings, Brennan touches Dale's drum set and a fight breaks out. Nancy and Robert suspend their television privileges for a week and demand that they find jobs or face eviction.
Brennan's arrogant younger brother, Derek, a helicopter leasing agent, visits with his family and humiliates Brennan and Dale. Dale punches Derek, which leads Brennan to reassess Dale, and for Derek's frustrated wife, Alice, to become attracted to Dale and they begin a secret affair. Brennan and Dale bond over their shared interests, particularly music. Nancy reveals that Brennan had stopped singing after Derek and his friends taunted him during a school musical. Robert arranges job interviews for Brennan and Dale, but they perform poorly and are attacked on their way home by juvenile bullies. Robert and Nancy then announce plans to sell the house with Derek's help, retire, and travel on Robert's sailboat. They also enroll Brennan and Dale in therapy and set aside money for deposits on separate apartments. Brennan becomes infatuated with his therapist, Denise, but she maintains professional boundaries.
At Derek's birthday party, Brennan and Dale show a promotional video for their proposed entertainment business, "Prestige Worldwide". The promo includes a music video they filmed on Robert's boat without his permission that ends with the boat crashing. With their plans to sail the world dashed, Robert and Nancy's marriage becomes strained, and at Christmas they announce their divorce. Brennan and Dale argue, blame each other, and move out separately. While living independently, each becomes more functional and productive.
Brennan asks Derek for a job at the helicopter leasing company, and later insists on running a major client event, the Catalina Wine Mixer. He hires the catering company where Dale works, reconciles with him, and invites Robert and Nancy to attend. During the event, the hired Billy Joel cover band quits after the lead singer overreacts to a heckler. Derek holds Brennan responsible and fires him. Robert, realizing that his rigid demands for Brennan and Dale to mature have stifled them, urges them to perform. They take the stage and Brennan sings "Por ti volaré" while Dale plays drums. Their moving performance prompts Robert and Nancy to reunite, improves Brennan's relationship with Derek, and triggers Denise's romantic interest in Brennan. Dale ends his affair with Alice.
Six months later, Robert and Nancy have remarried and returned to the house, while Brennan and Dale operate Prestige Worldwide as a small entertainment business providing karaoke services. Robert has turned his boat into a tree house stocked with props as a Christmas gift for Brennan and Dale. In a mid-credits scene, Brennan and Dale retaliate against the bullies.