Bring a large pot of salted water to a rolling boil. Add elbow macaroni and cook for 8–10 minutes, until al dente. Drain and rinse under cold water.

Finely chop the celery, red bell pepper, and red onion into bite-sized pieces.

In a mixing bowl, combine mayonnaise, apple cider vinegar, mustard, salt, and pepper. Whisk until smooth.

Add drained macaroni and chopped vegetables to the dressing, and gently fold until well-coated.

Cover and refrigerate for at least 1 hour to chill.

Stir before serving, and garnish with freshly chopped parsley if desired.