When I view the available hats on http://winterba.sh/ the shiver me timbers hat does not appear. The hat must be achievable as I have seen other users wearing it so why does it not display on the main winter bash page?
There are 'public' hats, and there are secret hats. Shiver Me Timbers is but one of the secret ones.
You don't get to see the secret hats until you've earned them!