Whisk the base. In a medium bowl, whisk together the mayonnaise, buttermilk, and sour cream until smooth and lump-free.
Add the herbs and spices. Stir in the chives, parsley, dill, garlic powder, onion powder, vinegar, salt, pepper, and sugar. Whisk until evenly combined.
Taste and adjust. Add more salt or pepper if needed. Thin with extra buttermilk or thicken with another spoonful of mayo to reach your preferred consistency.
Chill. Cover and refrigerate for at least 1 hour — overnight is even better. This is when the magic happens.
Serve. Give it a quick stir and enjoy with chicken tenders, fries, salads, or veggies.