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 in a blender; cover and 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.