Cut the jicama, watermelon, pineapple, and mangoes into uniform spears, about 1 inch thick by 4 inches long. Slice the cucumber into 1⁄2-inch thick rounds.
Toss the fruit in a large bowl with the key lime juice.
Distribute an even amount of fruit in eight 6-ounce cups, so guests can sip the juice after the fruit is gone.
Finish each with a generous sprinkle of sea salt flakes, chile-lime salt, and chamoy.