Place the frozen pineapple chunks into your blender. Add the coconut milk and pineapple juice, then sprinkle in crushed ice until the blender is nearly full. Secure the lid tightly.
Blend on high speed for about 30 seconds until the mixture is smooth, thick, and frosty. You should see a velvety texture with no large ice chunks.
Pour in 1 tablespoon of rum for a boozy version, then blend again for a few seconds to incorporate. Taste and add more rum if desired.
Check the consistency—if it’s too thick, add a splash more pineapple juice or a little water; if too thin, add a few more frozen pineapple chunks or ice and blend briefly.
Once the mixture is creamy, cold, and scoopable, pour it into a chilled glass or cup. Garnish with a pineapple wedge or cherry if you're feeling festive.
Insert a straw or spoon, serve immediately, and enjoy this tropical icy delight!