Cook the pasta according to package instructions and then drain well. Place hot pasta in a large bowl and sprinkle with the apple cider vinegar, stirring to coat. Let the pasta absorb the vinegar and cool for about 10 minutes.Meanwhile whisk together 1 cup mayo, 1 1/2 cups milk, brown sugar, salt and pepper. Fold the macaroni salad into the dressing, stirring to coat and then let cool completely.Add the remaining 1/2 cup milk and 1 cup of mayonnaise, along with any additional add-ins you would like, and stir to coat. Cover and refrigerate for at least 1 hour. Stir before serving. Enjoy!