On Christmas week, Rockhopper visites the island on CP or CPPS. Like all designs of Rockhopper, he has a Christmas hat OVER his pirate hat!
The Rockhopper's Santa hat is a bait item and can only be get by via cheating and on CPPS.
On UltimatePenguinv4. you can see a lot of penguins wearing it since the Rockhopper's hat is currectly blocked.
The ID for the item is: 1521