Continuity mistake: One night after work, when Willie in his Santa suit and Marcus in his elf outfit are having their usual bickering in the parking lot outside the department store, there are two pedestrians walking on the other side of the street behind the elf with one person bringing a cell phone to his ear; when the shot switches back to the elf after Willie the (bad) Santa delivers his lines, the same two people can be seen tracing their same steps behind Marcus, this time with the phone back to the ear again.
Continuity mistake: When Billy Bob Thornton comes back to his new job one day in a drunken stupor as usual, he slumps in his Santa seat half unconscious, with the shot from behind the chair showing Willie almost out of his Santa suit, fully exposing his white t-shirt underwear down past the shoulders. In the next shot from the front, with Bernie Mac towering over next to him and getting ready to carry him away while still talking to Marcus the elf, Willie is now fully covered in his red coat, messy as it may be.
Continuity mistake: When Billy Bob Thornton gets woken up by his alarm clock, note the bottles behind the alarm clock. The labels are facing forward. Cut to the close of of Billy Bob's hand hitting the clock, and the labels are facing to the left. When it cuts to full screen again, the labels are facing forward. This happens several times.
Continuity mistake: In the scene where Bernie Mac is going to take Willie to his car, Marcus says something to him and Bernie drops Willie. When he drops Willie he is on his back and close to the Santa chair. Bernie and Marcus begin to argue and after the argument there is a wide shot. Willie is now laying on his stomach further away from the chair.
Factual error: The last half of the movie is supposedly set in Phoenix, Arizona. Since I live there, it was obvious that none of the shopping centers, housing developments, street names, police car markings, or police uniforms were from Phoenix. They looked like they were possibly from Los Angeles.