Use a butter knife or small offset spatula to spread marshmallow fluff around the rims of glasses. Put shredded coconut in a shallow bowl, then dip the glass rims in coconut to coat them with the fluff.
In a large pitcher, mix coconut milk, tequila, triple sec, pineapple juice, and lime juice.
Add ice to the glasses and pour the margarita mixture over it. Enjoy!