It's almost time for Winter Bash 2017!
For several years now, Stack Exchange has run a holiday event called Winter Bash! It's a fun little event where users collect "hats" that you can wear on your avatars by doing various things (post on a certain day, get a question to a certain score, and things like that).
This year the event will start on December 13, 2017, and it'll run up to and including January 3, 2018. After that, the hats we've earned will all disappear.
Long story short . . .
(Note: Users who don't want to see hats will be able to click a button labeled "I hate hats".)