We do not normally advocate for specific brands of ingredients, but we would be remiss not to tell you that Mexican Squirt is truly the best grapefruit soda to use here. It is widely available at Mexican grocery stores and markets. If you cannot find it, Jarritos grapefruit soda is a decent substitute. To avoid using a soft drink altogether, substitute 2 ounces grapefruit juice, 2 ounces club soda or sparkling water, and 1 teaspoon Simple Syrup.
Run around the rim of a chilled rocks or cocktail glass:
Frost the rim of the glass with:
Add to the glass:
Stir, then fill the glass with ice cubes. Garnish with: