1Place 2 teaspoons sugar in a saucer. Rub the rims of 6 glasses with lime wedge, spin rim of each glass in sugar to coat. Set prepared glasses aside.
Combine watermelon, tequila, lime juice, triple sec, and remaining 2 tablespoons sugar in a blender, process until smooth. Fill each glass with 1/2 cup crushed ice. Add 1/2 cup margarita to each glass.
Garnish with lime wedges or melon balls, if desired.