Festivus
Let's start with the original, shall we? A 1997 episode of Seinfeld introduced us to Festivus, a holiday created and celebrated by George Costanza's father on December 23rd. It's easy to decorate for (a single aluminum pole is all you need, as tinsel is too distracting), and filled with catharsis. You start the festivities with an "Airing of Grievances," as you gather your family around, and tell them all the ways they have disappointed you over the past year. It ends in "Feats of Strength," which basically just involves some aggressive roughhousing. Ah, a Festivus for the rest of us!
[Photo via @toddgartland]