Preheat the oven to broil. Slice a grapefruit in half then sprinkle both halves with sugar. Side Note: Put a thicker layer of sugar on each half if you want a really caramelized crust.
Place on a baking sheet and put it on the middle rack to broil. Watch it very carefully so it doesn't burn.
Remove it from the oven once the sugar has caramelized, about 2-3 minutes. Eat immediately. Enjoy.