The 10 Least Successful Holiday Specials of All Time describes The Lost Star Trek Christmas Episode: “A Most Illogical Holiday” (1968):
Mr. Spock, with his pointy ears, is hailed as a messiah on a wintry world where elves toil for a mysterious master, revealed to be Santa just prior to the first commercial break. Santa, enraged, kills Ensign Jones and attacks the Enterprise in his sleigh.
I like the last paragraph:
Rumor suggests Harlan Ellison may have written the original script; asked about the episode at 1978′s IgunaCon II science fiction convention, however, Ellison described the episode as “a quiescently glistening cherem of pus.”