Put half of the red grapes and half of the white grapes in the freezer, for garnish. Put the remaining grapes in a large bowl and "smash" them with a whisk (or fingers).
Add the smashed grape to a large pitcher and pour in the grape juice and honey. Stir in about 16 ounces of vodka. Fill glasses about 1/2 full with the grape juice mixture and top with a splash of seltzer. Drop and few frozen grapes into each glass for a festive garnish that doubles as an ice cube!
I get wonderful local grape juices at my market at the same stand where I buy my grapes. I especially like white grape juice for this recipe but anything will work! For vodka, I love Ciroc because it matches the grape flavor profile of the drink but love the "classics" like Stoli just as much.