Make the Syrup
In a large jar with a tight-fitting lid, vigorously shake 2/3 cup sugar, 2 tbsp. grapefruit zest and water until the sugar dissolves, about 1 minute. Strain into a pitcher.
Mix the Drink
Add tequila, orange liqueur, 1 cup lime juice and pomegranate juice to the pitcher; stir.
Rim the Glass
Pour 2 tbsp. lime juice on a plate. Spread 2 tbsp. sugar and 2 tsp. grapefruit zest on another plate. Dip the rims of 8 glasses into the lime juice, then into the sugar and zest.
Fill the glasses with ice, then add the margarita. Garnish with a grapefruit twist.