It's hat season. They're here. It's underway. Everyone is buckled in and the rubber has hit the road. Pretty soon you'll start to notice the new WinterBash notification icon lighting up in your status bar:
When you've earned a hat you will see a notification, clicking on the link(s) contained within will take you to a Hats popup which will show you the hat(s) you've earned and allow you to choose to wear it on your avatar. It's as simple as selecting the various options available in the popup:
So what is this hat malarkey? It's a special festive/holiday season event run by the StackExchange crew, where doing certain things earns you a hat, you then get to select which one you want to wear.
What hats are there? Where's the list? You can find a list here. But be warned - there are a bunch of hats that are not on the list - they are a surprise. By all means post an answer here with a picture and a description of how you got it should you get one.
Woot I got the most awesome hat ever! Wear it with pride while you can - the hats get thoroughly deloused and put back in the closet on January 4th. Any with horns will have the horns polished ready for next year. Woolen ones will be de-pilled and de-linted. Earn it and wear it while you can.
Do I have to wear a stinkin' hat? No, nobody is forcing you to wear anything - just don't put it on. Or use the link illustrated above to remove it. If you really hate hats or just not a festive type, then you can opt out of the hat experience by clicking the I hate hats link in the notification dropdown: