Remove the flesh from 1 brown coconut, reserving the water. Peel off the skin and cut the flesh into small pieces. Transfer to a blender and add the reserved coconut water; puree until almost smooth. Bring the coconut mixture and 1 1/2 cups water to a boil in a saucepan, then remove from the heat and let stand 30 minutes; strain through a fine-mesh sieve and chill. For each drink, shake 1/4 cup of the mixture with 1/3 cup pineapple juice and 2 tablespoons spiced rum in a shaker with ice. Strain into an ice-filled glass.
TIP: For a frozen version of this drink, blend the cocktail ingredients with 1 cup ice.
Photograph by Kang Kim