1.Cut rind from watermelon. Cut watermelon flesh into 2cm (¾-inch) cubes, place in a zip-lock bag, freeze 1 hour or until ready to use.
2.Just before serving, half-fill a jug with ice cubes, then add frozen watermelon and mandarin rind. Stir vodka and sugar in a small bowl until sugar dissolves. Add vodka mixture to jug with remaining ingredients, stir until combined. Serve immediately.