They don't necessarily need to be Christmas themed movies but some that come to mind:

Jaws 4 (it's crazy that the first 20mins of this movie do take place during Christmas, with carolers, presents being opened by the tree and then it's all in the bahamas, such a weird film)

Rambo: First Blood (You see Christmas trees & decorations in the sheriffs office and then the ending is a shoot out on the street with Christmas lights)

Tangerine (sunny LA, barely even registers)

Lethal Weapon (Shane Black, need I say more) Kiss

Kiss Bang Bang (more Shane Black!)

We all know the argument about is Die Hard a Christmas movie and I say dammit it is, it doesn't just take place during Christmas but there are constant Christmas references throughout.

Anyway, what are some incidental Christmas movies?