Using lime wedges moisten the rims of six margarita or cocktail glasses.
Set aside limes for garnish. Sprinkle coarse sugar on a plate; hold each glass
upside down and dip rim into sugar. Set aside. Discard remaining sugar on plate.
In a blender combine the lemonade concentrate and raspberries; cover and
process until blended. Press mixture through a fine meshed sieve; discard seeds.
Return raspberry mixture to blender; add ice, strawberries, blueberries, sugar
and tequila if desired. Cover and process until smooth.
Pour into prepared glasses. Garnish with reserved limes.