Wonderful Christmastime is empirical proof that evil exists as a mensurate force in the world, independent of cognition and social constructs. I think the devil was guiding Sir Paul’s hands during its composition and my soul withers a little every time I hear it.
ETA- for sheer holiday awfulness though, nothing beats The Christmas Shoes. You get most the of the way through the song and you’re thinking, “Well that was horrible, but at least it can’t get any worse,” and BAM! that’s when the children’s chorus comes in.