To a blender add cubed watermelon. Pulse until liquefied. Strain through a fine mesh sieve.
Combine watermelon juice, vodka, triple sec, and lime juice in a cocktail shaker with ice. Shake until combined. Pour over ice in a highball glass. Serve and enjoy.
Notes
1 pound of cubed watermelon = about 3 cups
Remove any black seeds from your watermelon before blending. Soft white seeds are fine.
Vodka can be substituted with your favorite clear rum.
Optionally, garnish with fresh mint leaves, a cube of watermelon on the rim, or an orange slice.