Xmas

In the future, the word Christmas has been completely lost in the mists of time, and replaced with the word "Xmas", pronounced Ecks-Mas. As such, the day has lost all religious connotations it had in the past. As pines are extinct, palm trees are used. Being nude on Xmas seems to be quite popular. However, it is not wise to be outdoors after sundown on Xmas eve, because you'll probably be killed by Santabot.

The origins of Xmas are told in The Story of Xmas; a play about Ebenezer Omicronian who is visited by six ghosts who foretell the coming of Zombie Jesus and reveals the reason the holiday changed it's name. Mom is somehow involved.