Cut open two grapefruits.
Mix in some sugar, about 1/3rd of a cup, and some boiling water: about 1/4 a cup (to taste.) Pour into a baking pan.
Put in the freezer.
Freeze for a few hours.
Then scrape with a fork:
Serve in a wine glass, a short glass, or even a paper cup. The choice is yours. You will be happy, nonetheless.