Add the mayo, sour cream, milk, dill weed, dried parsley, garlic powder, onion powder, salt, a pinch of black pepper, and white vinegar to a separate bowl. Stir until smooth.
1/4 cup sour cream, 1/4 cup mayo, 1/4 cup milk, 1/2 teaspoon dill weed, 1/4 teaspoon dried parsley, 1/4 teaspoon garlic powder, 1/8 teaspoon onion powder, 1/8 teaspoon salt, pinch of black pepper, 1 teaspoon white vinegar