Rub a grapefruit wedge around the rim of a glass and then dip the glass into the salt, twirling the glass until the rim is well coated. Let the salt rim set for a minute or two.
Fill a lowball glass with ice cubes.
Pour the liquor (gin or vodka) and grapefruit juice into the glass.
Gently stir.
Garnish with the grapefruit wedge.
Notes
Gin and vodka work equally well in this cocktail recipe.
You can replace the grapefruit wedge with another citrus wedge. You can also add a rosemary sprig.