1. Place 2 teaspoons sugar in a saucer. Rub the rims of 6 glasses with 1 lime wedge; spin rim of each glass in sugar to coat. Set prepared glasses aside.
2. Combine watermelon and next 4 ingredients (through Triple Sec) in a blender; process until smooth. Fill each prepared glass with 1/2 cup crushed ice. Add 1/2 cup margarita to each glass. Garnish with lime wedges or melon balls, if desired.