Plot:
James King (Will Ferrell) is an extremely wealthy hedge fund manager, engaged to his gorgeous gold-digging fiancee Alissa (Alison Brie). His car washer, Darnell Lewis (Kevin Hart), and his wife, Rita, are trying to put their daughter Makayla in a better school away from the bad neighborhood they live in. James meets Darnell when the latter accidentally frightens James in the parking lot. James makes a speech about how he got to his success, and to inspire Darnell to go for his. He pulls out a big wad of cash, only to give two singles as a "tip" for Darnell.
Alissa hosts an engagement party for herself and James. She gives him an electric guitar as a gift, and invites John Mayer onstage to perform. James performs alongside Mayer momentarily until the FBI storm in and arrest James for fraud and embezzlement. James's lawyer Peter Penny urges James to go for a guilty plea, but he refuses and insists that he will be exonerated. Instead, everybody that lost money in the embezzlement scheme is out for James's head. The judge finds him guilty and sentences James to ten years at San Quentin, with only 30 days to get his affairs in order. His assets are frozen and he is placed under house arrest. He cuts off his ankle monitor and tries to flee the country. He drives to a country club to get Alissa to go with him, but she says she has left him and decided to move on. The police then show up and arrest James, who asks his boss, Alissa's father, Martin (Craig T. Nelson) for help.James encounters Darnell once more in the parking lot, expressing his fears over going to prison. He asks Darnell how he managed in prison, simply assuming he was incarcerated because he is black. James then begs Darnell to teach him how to toughen up if he wants to survive in prison. Darnell demands payment in the form of $30,000, which James agrees to.
Darnell, who has little idea of how to act tough himself, tries to put on a facade of his own. To start his "training", Darnell pepper-sprays James upon arriving to his home. He tries to get James ready for prison by intimidating with his "mad dog" face (James can only "sad dog" it), creating scenarios in which he must defend himself, and picking fights at the park (only for James to be beaten multiple times). James gets in touch with Martin and says he's getting help. Martin, who is the actual crook, thinks James is onto him and orders Peter and a hired gun named Gayle to take care of business.
With little time left and even less improvement, Darnell figures that James has to learn how to perform oral sex in prison. They go to a gay hook-up spot for James to find a man to give fellatio to, but he can't go through with it and tells Darnell (in front of the other curious and interested gay men) that he will keep going and do whatever it takes to "get hard." James starts to work out harder and faster, makes shivs, and learns "keistering" - smuggling contraband in the anus. Darnell simulates a prison raid with help from James' personal workers acting as inmates. In the chaos, James gets a shiv stuck in his head. Darnell drives James to his home for Rita to get the shiv out. He has dinner and listens to Darnell make up a story of how he went to prison (which is just a retelling of Boyz n the Hood). Rita asks Darnell why he can't just find the real criminal to help James.
Mere days before his incarceration, James and Darnell resolve for James to join a local gang, the Crenshaw Kings, to protect him in prison. James dresses in a ridiculous outfit that gets unwanted attention. Darnell's cousin Russell (T.I.), who runs the gang, isn't convinced that James can pay him and knows that Darnell is lying about prison. James does help the gang gain interest in finance and stocks. Darnell drives James to a bar where the Alliance of Whites gang is based. James is unable to be a convincing racist, leading the white supremacists to think he's a cop. They nearly burn his face with a motorcycle tire until Darnell rescues him by bursting in with a flamethrower. Darnell realizes James is innocent and they conclude that Martin is the crook. They sneak into his home and find the embezzlement records on Martin's old computer. Unfortunately, Gayle finds them and takes the computer back after telling James that Darnell has a clean record and never actually went to prison. Despite his earlier misjudgment of Darnell previously being in prison, James feels betrayed and leaves the parking lot.
James returns to the Crenshaw Kings with the intention of joining. For his initiation, they want him to kill someone. Darnell arrives in time to stop him and convince him to catch Martin and expose him. The two find Martin's yacht and sneak on board. They grab the computer, only to come across Gayle and more hitmen. James unleashes a series of capoeira moves on the goons while Darnell protects the computer. Martin comes out and confesses to the crime, while Alissa steps out and admits that she got in on the scheme. Martin and Alissa try to convince James to run away with them, but he turns them down and heads to the life raft with Darnell. The duo tries to get out on the life raft until Gayle shoots it out. James pulls out a gun he kept up his rear and aims it at Gayle until the cops show up just in time, in response to James being outside of the county lines. Martin, Alissa, Gayle, and Peter are all arrested. James is also arrested for pulling out the concealed weapon, but he only serves six months. He helps the police return the stolen money and decides to give Darnell money to expand his car wash business and move to a better neighborhood. After the six months are up, Darnell goes to pick James up from prison and the two ride off.