Whisk together vinegar, mustard, oregano, Italian seasoning, red pepper flakes, sugar, salt and black pepper in a medium bowl.
¾ tsp kosher salt, ½ tsp freshly ground black pepper, ⅓ cup red wine vinegar, 1½ tsp Dijon mustard, ½ tsp dried oregano, ¼ tsp Italian seasoning, ⅛ tsp crushed red pepper flakes, ¾ tsp granulated sugar, ½ tsp kosher salt, ⅛ tsp freshly ground black pepper