Whisk together vinegar, mustard, oregano, Italian seasoning, red pepper flakes, sugar, salt and black pepper in a medium bowl.
1/3 cup red wine vinegar, 1½ teaspoon Dijon mustard, ½ teaspoon dried oregano, ¼ teaspoon Italian seasoning, 1/8 teaspoon crushed red pepper flakes, ¾ teaspoon granulated sugar, ½ teaspoon kosher salt, 1/8 teaspoon freshly ground black pepper