Bad Santa is a 2003 film directed by Terry Zwigoff, produced by Joel and Ethan Coen, and starring Billy Bob Thornton as the title character and Tony Cox (best known for Friday and Me, Myself and Irene) as his partner-in-crime. Bernie Mac, John Ritter, Lauren Graham, Lauren Tom, Ethan Phillips, Brett Kelly and Cloris Leachman are also featured. The unrated version of the film was released on DVD in 2004 as Badder Santa.

The story principally concerns two con men, miserable Willy (Thornton) and foulmouthed Marcus (Cox), who, each Christmas season, seek work at a different shopping mall dressed as Santa Claus and one of Santa's elves. Rather than spreading good cheer, the duo's motive is to rob each establishment, with Marcus disabling the security systems each year and Willy cracking the safe. The strategy becomes complicated when Willy encounters an 8-year-old boy who he meets and ends up moving in with. Through their interaction, the boy (Brett Kelly) inadvertently teaches Willy the true meaning of Christmas. In addition to being a criminal, Willy is also a bitter and abusive drunk as well as a sex addict and it only seems to worsen each passing year, thus putting a bitter strain on his partnership with Marcus.

The movie attracted bad publicity before its release from critics who likened the movie to an "evil twin" of Miracle on 34th Street and chided The Walt Disney Company for allowing such a beloved figure as Santa Claus to be trashed by its Miramax subsidiary.

Fans of the film, however, counter that it is good for those who have in some way fallen through society's cracks to have a Christmas film that reflects what Christmas really means for them. Also of delight to those disheartened with Christmas is Willy's relationship with Therman. The mainstream figures beloved by those chiding Miramax and Disney for Bad Santa are cited by many survivors of abuse as being most likely to abuse characters such as Therman.

The film was John Ritter's last live-action role—he died prior to its release—and it is dedicated to him.