In 1979, a hot day in the city finds a whole neighborhood of kids and adults relaxing out doors on the street. A nerdy young boy in love with a beautiful girl is about to receive his first kiss. Just then, the local bully yanks down the boy's shorts and underwear, humiliating him to the laughter of the entire crowd.
In the present, timid businessman Dave Buznik (Adam Sandler
) works for a pet clothing company in New York City. His abrasive boss Frank Head (Kurt Fuller
) takes credit for Dave's money-making work and steps on him in return. His loving girlfriend, Linda (Marisa Tomei
) is supportive but wishes he would stand up for himself. Her college friend, Andrew (Allen Covert
), wants to date her and treats Dave like a loser. Dave just wants to avoid conflict (and any hint of public affection.)
When an inflight misunderstanding with a stewardess goes haywire, Dave is ordered by Judge Daniels (Lynne Thigpen
) to undergo anger management therapy at the hands of unorthodox specialist Dr. Buddy Rydell (Jack Nicholson
At his first anger management group meeting, self-effacing Dave is certain he doesn't belong there and asks Buddy to let him out of the course. Odd and volatile characters such as Nate (Jonathan Loughran
), Lou (Luis Guzmán
), and Chuck (John Turturro
) startle him. Buddy pushes Dave hard until Dave actually starts shouting. At the end of the meeting, Buddy says Dave needs to be there. He also arranges for him to pair up with eccentric Chuck for mutual support.
As Dave prepares for a romantic evening with Linda, Chuck turns up on his doorstep and insists Dave fulfill his support duties. They go to a restaurant, Chuck picks a fight for no reason ... and Dave ends up back in court on charges of assaulting a waitress and a blind man (Harry Dean Stanton
). Judge Daniels orders Dave to step up his therapy or wind up in jail. Buddy decides to move in with Dave for intensive treatment.
Buddy's obnoxious behavior includes everything from throwing out Dave's CDs, nudity, sleeping with Dave in his bed (and farting), throwing food when it's not done his way, flirting with Dave's girlfriend, and pissing off Dave's boss. He forces Dave stop driving on the way to work in order to sing the show tune "I Feel Pretty", while blocking traffic on a bridge. He takes Dave to a street corner and pays a transvestite (Woody Harrelson
) to get in the back seat with Dave. Dave is horrified, and finally starts yelling and demanding that the shemale get away from him. Buddy explains that this is an important step forward in the program: righteous anger.
Dave and Buddy go to Boston to see Buddy's mom. At a bar, Buddy lures Dave into hitting on a beautiful girl (Heather Graham
) using a crude pickup line. To his shock, she takes the bait. When he looks around, Buddy has left him and he doesn't even know where to go. The girl takes him home and tries to seduce him, and turns violent when he refuses because of his commitment to Linda. She throws him out in the rain where he screams back at her.
On their return trip from Boston, Dave falls asleep. When he wakes up, Buddy has taken him to an out of the way Buddhist sanctuary. His old nemesis Arnie Shankman has become a monk. Buddy incites the two to fight, and finally their anger ignites. Dave discovers the heady feeling of a little righteous revenge.
When he meets with Linda, Dave tries to nerve himself up to propose to her but is unable to do so. Recognizing the lost moment, she says that Buddy has advised that they separate for a while. Dave is devastated, but Buddy assures him things will be fine. When he learns that Linda will be going out to a swank restaurant with some guy, Dave decides to show up with the two porn star girls (Krista Allen
and January Jones
) from his anger management class. The scantily clad girls accompany him in ... where he finds out that Linda's date is Buddy himself. Buddy swears he is dating her for Dave's benefit, that nothing is going on. But later that night Buddy confesses that the date led to kissing and then announces that he and Linda are in love. Dave loses it and leaps for Buddy ... and Dave is back in court as the judge finds him incurable, promising that at his sentencing he will be going to prison. A bruised, battered and bandaged Buddy is present, accompanied by Linda. Dave sees the two enter a taxi outside (and Buddy removing his neck brace!), as Linda gazes at Dave regretfully.
Dave finds out that Buddy is taking Linda to a Yankees game, and realizes that Buddy is about to steal his proposal "idea" (having it appear on the marquee). He rushes to the stadium to prevent this disaster. Guards try to stop him as he storms on to the field and appropriates the microphone to plead with Linda not to marry Buddy, that Buddy is crazy. Dave admits that he was an angry guy, that letting people step on him was wrong. He tells Linda that he loves her and wants to marry her.Linda agrees, but on the condition that he kiss her in front of everyone in the stadium. He hesitates, but finally gathers his courage and does it. Amazingly, the loving message appears on the marquee, and Linda happily tells him that he just graduated from anger management! Waiting for the train home, she explains that she'd read Buddy's book and asked if he could help Dave. The stewardess, the judge and many others were in on the plot to help Dave find and express his anger.
A celebration party in the park with the whole anger management class is interrupted by a man with a gun. Dave stands up to him and refuses to be afraid, while everyone else begs him not to be a hero and get himself killed. The gunman fires - his water pistol, as the whole thing turns out to be Dave's prank revenge on everyone for duping him.