All together now, in your creepiest voices!

"Santa Claus is coming... to town..."

Seriously, though.  Read the lyrics.  If they didn't use a creeped up version of this song in Silent Night, Deadly Night, well... they should have.* 

(first link via Rocketboom)

*It's been way, way too long since I've seen it.  The scene where the shorts-wearing -- yet topless -- girl is chased by poor-crazy-nun-hating-Santa-suit-wearing-orphan-man-whose-parents-were-brutally-murdered-by-a-man-in-a-Santa-suit-thus-leading-to-his-Christmas-freakout and then IMPALED on a set of antlers -- classic.