Remove top from a fresh pineapple, and then cut in half widthwise. Create 2 cups by cutting and scooping the flesh out from each half pineapple. Place 1 cup of that flesh, chopped, 3 oz. rum, 1/3 cup coconut milk and 1 1/4 cups pineapple juice in a blender and puree. Pour mixture into your cups, add some ice cubes, and serve.