You'll need:
1 cup fresh watermelon chunks, preferably seedless
2-3 rounds fresh lime, quartered
5 mint leaves, with stalk if desired
2 oz golden rum (or vodka!)
Sprig of mint and round of lime for garnish
Layer the watermelon, lime, and mint in a cocktail shaker. Muddle until the watermelon is completely juice and pulp. Add ice and rum, and shake to chill. Strain into a chilled glass and garnish with a round of lime and sprig of mint. Enjoy!