First, line the rim of a can of sparkling water with lime, and dip the top of the can into some sugar (optional). Then, open the can and drink about half a can of lime sparkling water (or pour half into a cup and make a drink for a friend! You just need some room here for all the other good stuff).
In a small bowl, muddle together the simple syrup and a couple mint leaves until the mint has released its oils. Add the mint simple syrup, white rum, and pineapple juice to the can. Gently swirl to combine. Garnish with mint and lime, and enjoy!