Dave Buznik (ADAM SANDLER) is a mild-mannered executive assistant at a pet products company who lets his boss, Frank Head (KURT FULLER), take credit for his work, has a problem showing public affection for his girlfriend, Linda (MARISA TOMEI), and won't stand up to her former boyfriend, Andrew (ALLEN COVERT), who keeps hitting on her.
Thus, he's shocked when he's charged for assaulting a flight attendant during an airline trip where he allegedly lost control of his temper. Accordingly, and despite the efforts of Dave's lawyer, Sam (KEVIN NEALON), Judge Daniels (LYNEE THIGPEN) sentences him to twenty-hours of sessions with anger management therapist Dr. Buddy Rydell (JACK NICHOLSON).
At a group gathering, Dave meets Buddy's other patients including Lou (LUIS GUZMAN), Chuck (JOHN TURTURRO) and porn stars Stacy (KRISTA ALLEN) and Gina (JANUARY JONES). When Chuck gets Dave involved in a barroom brawl, Judge Daniels wants to sentence Dave to a year in prison, but Buddy intervenes and moves in with him for 30 days of intensive therapy.
From that point on, and as Buddy makes Dave go through a series of unorthodox therapeutic sessions, including an encounter with a "she-male," Galaxia (WOODY HARRELSON), the formerly mild-mannered man becomes increasingly irritated and angry as his entire life is turned upside down.