For the candied coconut: In a dry skillet or saucepan, toast the coconut over medium-low heat, stirring frequently, until the flakes are mostly golden in color. Remove from the heat and immediately add the chili powder, agave nectar and salt. Stir until the mixture is combined, then let the coconut cool completely before transferring to a bowl.
For the pineapple soft serve: In a food processor or blender, combine the frozen pineapple, coconut milk, agave, lime juice and salt and pulse until the pineapple is finely chopped. Then process or blend, stopping to scrape down the sides of the bowl/jar as needed, until smooth and airy, 3 to 4 minutes. Serve immediately or transfer to a resealable top plastic bag and freeze until just firm, about 20 minutes. Trim off the corner of the plastic bag and pipe the mixture into serving bowls, soft serve–style. Garnish with the candied coconut and a float of dark rum if desired (and 21+).