Residual urine that is present on an individual after using the bathroom. Because of its sometimes sticky nature, it is attributed to being the juice of a watermelon that was supposedly recently consumed by the individual.
Person 1 is shaking hands with Person 2 who has just walked out of the bathroom.
Person 1: "Why are your hands so wet and sticky?"
Person 2: "That's just some watermelon juice from my lunch."