The Grass Skirt Vendor is located on Booga Bay on Shark Tooth Island. He helps you on your quest.
The Grass Skirt Salesman has puffy, curly orange-brown hair. He wear square glasses with transition lenses with darker black frame around the corner. His face is covered with freckles. He wears white T-shirt with a blue tie that has light blue stripes on it. He wears a green grass skirt and long green pants (if you look closely). His eyes are narrow. He has light yellow orchard skin.
Once you find him, talk to him and he will say, "Take a spiffy grass skirt. You'll look like a native islander!" He will then give you a Grass Skirt for free. After that, if you talk to him he will say,"You'll look like a native islander with that skirt!" He also continues to stand at his stand, waiting for other customers.
You need the grass skirt in order to the Medicine Man. He only talks to native islanders. If you wear the skirt, you will look like a native islander, just like the Grass Skirt Vendor advertises.