In a medium bowl, whisk together the buttermilk, sour cream, mayonnaise, garlic, white vinegar, sugar, salt, and black pepper until smooth.
Gently fold in the blue cheese crumbles and chopped chives, leaving some larger chunks if desired.
Taste and adjust seasoning with additional salt, pepper, or vinegar.
Cover and refrigerate for at least 30 minutes before serving for best flavor.