Buddy Buddy is a 1981 American comedy film based on Francis Veber's play Le contrat and Édouard Molinaro's film L'emmerdeur. It is the final film directed and written by Billy Wilder.

To earn his long-awaited retirement, hitman Trabucco eliminates several witnesses against the mob. On his way to his last assignment, Rudy "Disco" Gambola, who is about to testify before a jury at the court of Riverside, California, he encounters Victor Clooney, an emotionally disturbed television censor who is trying to reconcile with his estranged wife Celia.

Trabucco takes a room in the Ramona Hotel in Riverside, across the street from the courthouse where Gambola is to arrive soon. As chance would have it, Victor moves into the neighboring room at the same hotel, and after he calls Celia and she rejects his attempts at a reconciliation, he tries to kill himself. His clumsy first attempt alerts Trabucco, and fearing the unwelcome attention of the police guarding the courthouse, he decides to accompany Victor to quietly eliminate him, but he is repeatedly foiled by a series of inconvenient happenstances.

Trabucco and Victor drive to the nearby Institute for Sexual Fulfillment, the clinic where Celia, a researcher for 60 Minutes, has enlisted because she has become enthralled with the clinic's director, Dr. Hugo Zuckerbrot. After Celia spurns Victor again, they return to the hotel, where Victor plans to jump off the building after setting himself on fire. While trying to stop him, Trabucco accidentally knocks himself out and Victor, having a change of heart, brings him back inside and tries to take care of him. Meanwhile, Zuckerbrot and Celia devise a plan to have Victor confined in a mental institution; Zuckerbrot arrives at the hotel and after mistaking the injured Trabucco for Victor, injects him with a potent sedative.

With Gambola's arrival imminent, Trabucco attempts to fulfill his contract but is too groggy to make the shot. After seeing him assembling his rifle and learning Trabucco's true profession, Victor volunteers to take out Gambola to help his new "best friend". Victor succeeds, and the two escape the police after Trabucco, posing as a priest, has made sure that Gambola is dead, but he refuses Victor's company and heads off alone.

Months later, Trabucco enjoys his tropical island's retreat until he is unexpectedly joined by Victor. Victor explains that he is wanted by the police after blowing up Zuckerbrot's clinic, and Celia has run off with the doctor's female receptionist. Desperate to get rid of the irritating Victor, Trabucco suggests to his native servant the possibility of reviving the old custom of sacrificing humans in the local volcano.

L'emmerdeur, a huge hit in Europe, had been released as A Pain in the Ass in art houses in the United States, where it had enjoyed moderate box-office success. Jay Weston of William Morris Agency obtained the remake rights and pitched on the film for Matthau, Lemmon and Wilder to work.

Wilder said of the film, "If I met all my old pictures in a crowd, personified, there are some that would make me happy and proud, and I would embrace them ... but Buddy Buddy I'd try to ignore."