I loathe with a passion Santa Claus is coming to town. "You'd better watch out, you'd better not cry..."
Most definitely Last Christmas. You know it's going to be that one before the words even start.
I wish it could be Christmas every day.
Here it is merry Christmas, especially with that screeched line "IT'S CHRISTMASSSSSS!"
Sad songs, such as Christmas shoes, the little boy that Santa Claus forgot. And there's a really terrible one: the Cat Carol, it is the saddest Christmas song ever, especially if you love cats. (Listen to it at your peril - it makes grown men cry.) Another reason I loathe Last Christmas.
Any over-slow ones, like "chestnuts roasting on an open fire". Prolongs the agony.
Ones which aren't really about Christmas, such as Sleigh Ride. I suppose Jingle Bells is one such as well.
Most pop versions of traditional carols. I love proper choral carols (except away in a manger, as it's so overdone), but the ones with a solo pop star voice, especially if they mess about with the rhythm - just no.
I despise Mistletoe and Wine for a different reason. I was once involved in a church pantomime, which had music between the scenes; once scene had a particularly complicated set up, which had to be rehearsed again and again, so we heard that song again and again.