Cook the elbow macaroni in a large pot of salted boiling water for 8-10 minutes until al dente. Drain and rinse under cold water.

In a mixing bowl, combine mayonnaise, yellow mustard, white vinegar, black pepper, and white sugar. Whisk until smooth.

Finely dice red onion, celery, and green bell pepper. Soak the onion in cold water to reduce sharpness.

In a large bowl, combine cooled macaroni with half of the dressing. Toss and fold in chopped vegetables.

Cover and refrigerate for at least 2 hours to let flavors meld. For optimal flavor, chill overnight if possible.

Before serving, stir the salad and add the remaining dressing to taste. Adjust seasoning if necessary.