Mine is "Mary Did You Know"....I like Kenny Rogers and Wynonna's version best.
@Glis -- One reason I like Spinal Tap's "Christmas with the Devil" is because many popular music groups over the years have sung about sex and drugs and rock and roll....until it came time to make a little extra cash selling a Christmas music album. Then, suddenly, they were about peace on Earth and goodwill towards all mankind.
I think the Spinal Tap approach is more honest...;-D...