Step 1: Prepare the watermelon. Cut your seedless watermelon into uniform 1-inch cubes and set aside in an airtight container.
Step 2: Create the Jolly Rancher infusion. Unwrap and crush the watermelon Jolly Ranchers. In a small saucepan, combine the crushed candies with 1/4 cup water and 1 cup white rum. Heat over low to medium heat, stirring constantly, until the Jolly Ranchers are completely dissolved and a smooth syrup forms. Do not boil. Remove from heat and let the syrup cool completely to room temperature.
Step 3: Infuse and chill. Once the Jolly Rancher syrup is cool, pour it over the watermelon cubes in the airtight container. Ensure the watermelon is mostly submerged. Cover the container tightly and refrigerate for a minimum of 4-6 hours, or preferably overnight, allowing the watermelon to absorb the flavors.
Step 4: Serve chilled. Remove the infused watermelon bites from the refrigerator. Serve them cold, optionally garnished with fresh mint leaves for an extra touch of freshness.