The holiday of Zappadan was founded to celebrate the life and times of that prophet of rock'n'roll, Frank Zappa.
This prophet has not been dead twenty years, but he already upholds the truism that a movement's followers will schism after the founder is dead. There are two camps of Zappadan, the twenty-firsters, who say Zappa was born on December 21st, and the twenty-seconders, who contend he was born on December 22nd. Sadly, the twenty-firsters seem to hold sway both at Wikipedia and at frankzappa.com. Both camps do agree that the holiday begins on December 4th, the date of his death, in an all-night rock party beginning at sundown on December 5th and continuing until the sun comes up or the cops are called.
Observers refrain from cutting their hair for the duration; instead, the men cultivate their mustaches and goatees. Some go so far as to post videos on their websites, one every day of the observation.