Preheat oven to 375°F. Prepare a muffin pan with 12 regular size cups by greasing them with non-stick cooking spray or use paper or silicone muffin/cupcake liners.
In a large mixing bowl, use an electric mixer to cream the butter and sugar together until light and fluffy. Beat in the egg, sour cream, and rum extract.
In a small mixing bowl, whisk together the flour, baking powder, baking soda, and salt. Stir the dry mixture into the wet mixture, just until combined. Fold in the pineapple and coconut.
Fill the 12 cups of the prepared muffin pan cups with the muffin batter, filling each cup about two-thirds full.
Bake the muffins at 375°F for 22-25 minutes, or until a toothpick inserted into the center comes out clean.
Cool the muffins in the pan for 5 minutes, then remove from the pan and cool on a wire rack.