Place 2 tablespoons flaked sweetened coconut in a small nonstick skillet over medium heat. Cook, shaking the pan often, about 4-5 minutes or until coconut lightly browns. Transfer to a bowl, and cool. Combine 1 1/2 cups cubed fresh pineapple, 1 cup pineapple juice, 3/4 cup light coconut milk (don't rinse measuring cup--see why below), 1/3 cup sugar, 1/4 cup light rum, and 8 ice cubes in a blender. Process until thick and smooth.
Dip a pastry brush or folded paper towel into the residual coconut milk in the measuring cup, and brush the inside and outside rims of 4 tall glasses. Dip the rim of each glass in the coconut to coat. Divide the piña colada among the 4 glasses. Garnish with pineapple, if desired.