This hat is located at Coop's house, by the Cinco de Mayo Shop, found on the map below.
http://i50.tinypic.com/24q5tzl.png (Unsupported image host)
Once you enter the house go up and turn right into the next room.
http://i50.tinypic.com/2j3haxd.png (Unsupported image host)
Once you have entered that room go downwards and you should find the hat in the bottom left corner.
http://i49.tinypic.com/w8q92c.png (Unsupported image host)

This hat is located in the northern part of the map by Amy's Hat Shop, found on the map below.
http://i48.tinypic.com/14ljyh.png (Unsupported image host)
Once you enter the house, you will find multiple different colored doors.
The door you want to enter is the blue door.
You will then reach the next room with more doors and you want to enter the green one and then pink, then blue, then green.
Once you enter the final door, you will find the giant snk.
http://i46.tinypic.com/2zz83dg.png (Unsupported image host)
Kill him and you will earn the hat!