Bad Santa (2003)

Terry Zwigoff’s Bad Santa (2003), starring Billy Bob Thornton, is a pitch-black Christmas comedy about a foul-mouthed conman who poses as a mall Santa to rob department stores. As his schemes fall apart, he forms an unlikely bond with a lonely kid, balancing crude humor with unexpected heart. It's one of the most iconic anti-holiday comedies of the 2000s.

Från IMDB:
A miserable conman and his partner pose as Santa and his Little Helper to rob department stores on Christmas Eve. But they run into problems when the conman befriends a troubled kid.