For dessert, watermelon takes on the classic Mexican pairing of chocolate and cinnamon, as well as zesty lime.
Stir sugar, cayenne pepper, cinnamon, and salt in a small dish; set aside.
Divide watermelon among 8 glasses; Tuck a piece of chocolate, a lime wedge, and a cinnamon stick into each glass. Refrigerate, covered, until ready to serve, up to 4 hours. To serve, sprinkle each with 1/2 teaspoon sugar mixture. Serve with remaining sugar mixture on side.