Add all of the ingredients into a cocktail shaker with ice.
Shake for vigorously for 30 seconds. This is a crucial step when making the cocktail. The water from the ice needs to melt while shaking so dilute the cocktail so the ingredients blend together.
Once the cocktail has been shaken, strain into a glass filled with ice.
You can use large ice cubes or crushed ice for this cocktail.
Notes
Use a good-quality dark rum for the richest flavor. Aged or blackstrap rum adds depth that balances the sweetness and bitterness.
Chill your glass ahead of time if you want an extra refreshing experience.
Fresh pineapple juice makes a big difference in flavor, but canned works in a pinch.
If Campari is too bitter for you, try using Aperol or reduce the amount slightly.
Make it ahead: You can batch this cocktail (without ice) and store it in the fridge for up to 24 hours—just shake with ice before serving.