Dip the rim of each high ball glass into simple syrup and then dip into toasted coconut flakes. To toast the coconut, place coconut on a baking sheet in a single layer. Place under the broiler for a few minutes, toss coconut with a spatula. Keep a close eye on the coconut as it toasts quickly! Set prepared glasses aside.
In a cocktail shaker, add lime juice, mint and simple syrup.
Use a muddler and gently press down and twist the ingredients together. The object is to release the oils and fragrance from the mint leaves. If you don't have a muddler, the back of a wooden spoon will suffice.
Add ice, pineapple juice and coconut rum to the cocktail shaker and shake vigorously until cold.
Add ice to prepared glasses and strain mixture into the glasses, dividing evenly.
Top with club soda.
Add a few fresh mint leaves to the glasses if desired and garnish with a fresh mint sprig.