Use a sharp kitchen knife and cutting board to peel and dice the pineapple into small, uniform cubes, then transfer them to a mixing bowl.
Slice the watermelon into cubes about the same size as the pineapple, then add them to the bowl with the pineapple pieces.
Drizzle the fresh lime juice over the diced fruit mixture, then gently toss using a spoon or salad tongs until evenly coated and combined.
Transfer the mixed fruit to a serving dish or bowl, and optionally chill in the refrigerator for 10 minutes to enhance the aroma and flavor.
Serve the fruit salad immediately, observing its vibrant color, juicy appearance, and fragrant aroma.