"Happy Festivus" is the traditional greeting of Festivus, a holiday featured in the Season 9 episode of Seinfeld named "The Strike", which first aired on December 18, 1997. Since then, many people have been inspired by this zany, offbeat Seinfeld holiday and now celebrate Festivus as any other holiday.
According to the Seinfeld model, Festivus is celebrated on December 23rd. However many people celebrate it other times in December and even at other times throughout the year.
The slogan of Festivus is "A Festivus for the rest of us!" The usual holiday tradition of a tree is manifested in an unadorned aluminum pole, which is in direct contrast to normal holiday materialism. Those attending Festivus may also participate in the "Airing of Grievances" which is an opportunity to tell others how they have disappointed you in the past year, followed by a Festivus dinner, and then completed by the "Feats of Strength" where the head of the household must be pinned. All of these traditions are based upon the events in the Seinfeld episode, Strangely enough, our Festivus traditions also have roots that pre-date Seinfeld, as it began in the household of Dan O'Keefe, a television writer who is credited for writing the Seinfeld episode.