Place 2 teaspoons sugar in a saucer. Rub rims of 6 glasses with 1 lime wedge; spin rim of each glass in sugar to coat. Set prepared glasses aside.
Combine watermelon and next 4 ingredients (watermelon 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 each glass with a lime wedge, if desired. Serve immediately.
Note: Add 2 to 3 drops of red food coloring to blender for a deeper red coloring, if desired.