Flower Hat is Clothing that you can get when you find a secret room in the 
Caves.
Go 1 room down from the Stomp Your Feet room.
From the entrance you come out of, follow the pathway north-east. About half-way through this path is a long leafy vine on the wall that has a small stone pathway at the base of the vine.
Follow the stone pathway down. You will not be able to see where you are, but you can use the camera's shifting perspective to help guide your way around to the southern entrance of the small room where the green Glyptodon is. Talk to Don, the Glyptodon, and you will be gifted the 
Flower Hat
Unlock Requirements[]
You will require: the Owl Totem, 
Obsidian Axe, and 
Obsidian Hammer to reach the room of the Caves where this item is located.