If using sugar for rim, pour a little bit on a small plate. Brush some grapefruit juice around the rim of your cocktail glass and place glass upside down in sugar to coat rim.
In an ice-filled cocktail shaker, add freshly squeezed grapefruit juice and grapefruit vodka. Shake well and pour into ice-filled cocktail glass.
Top with grapefruit seltzer and add a grapefruit wedge garnish onto the side of the glass.