I don’t want to bump Die Hard off the list, but I’d say that It’s a Wonderful Life beats it as a Christmas movie. I guess only the frame of the story is really set on Christmas Eve, though.
Don’t worry, Die Hard is not a Christmas movie.
It is in my house, my family gathered around and watched the movie on Christmas eve this past Christmas and I have watched it every Christmas for years and it all takes place on one Holiday so I don’t see why it shouldn’t count.