1 tablespoon white sugar
1 cup ice, or as needed
2 fluid ounces Ruby red grapefruit juice
1 fluid ounce vodka
1 fluid ounce triple sec
Pour sugar onto a small plate. Wet the rim of a martini glass with cold water; dip rim in the sugar to coat.
Fill cocktail shaker with ice; pour in grapefruit juice, vodka, and triple sec. Cover shaker with lid and shake. Strain and pour mixture into prepared martini glass.