Definitely "I saw mommy kissing Santa Claus". Hate it with a passion.
Actually, that goes for all the mawkish over-sentimental 'happy family' Christmas songs.

Can't stand "Little drummer boy". Our son Stephen The Drummer loathes it.

"Grandma got run over by a reindeer" is another, and the various follow-ups to it as well.

Songs about winter but not about Christmas. That includes "Jingle bells", "Sleigh ride" etc. As for "Winter wonderland"....

That will do for a start. Bah humbug, and thank you for listening.