Fill a cocktail shaker with ice cubes. Add the dark rum, pineapple juice, orange juice, and cream of coconut to the shaker.
Shake the mixture vigorously for about 20 seconds to thoroughly blend the ingredients and chill the cocktail.
Fill a highball glass or tiki mug with fresh ice cubes. Strain the cocktail mixture from the shaker into the glass or mug.
Garnish your Painkiller cocktail with a sprinkle of freshly grated nutmeg. You can also add a pineapple wedge or cherry for decoration.