01 - Combine chilled pineapple juice, coconut milk, and rum (if using) in a medium pitcher. Stir thoroughly until evenly mixed and slightly frothy.
02 - Add two scoops of ice cream to each of two tall glasses.
03 - Distribute the pineapple-coconut mixture evenly over the ice cream in both glasses.
04 - Crown each float with toasted coconut flakes, a maraschino cherry, and a pineapple wedge.
05 - Serve promptly with a straw and a long spoon.