Muddle mint leaves with white rum and the juice from lime wedge (1/8th of the lime). Muddling is done by lightly crushing the mint (just until the leaves bruise) using a mortar and pestle, a muddler, or whatever you have on hand (a small wooden spoon would work just fine). Just don't shred the mint! Run the squeezed lime wedge around the rim of the glass, then dip the top of the glass in a shallow plate of granulated sugar to coat the rim. Pour the muddled mixture into your glass, fill with crushed ice, and top off with the diet soda. Cheers!