Whisk together. While the elbow macaroni is draining combine the mayonnaise, white vinegar, sugar, mustard, and sweet relish in a small bowl and whisk together.
Toss together. Add the cooked macaroni, red onion, red bell pepper, and celery to a large bowl. Pour the mayonnaise mixture over everything and gently toss together until well coated.
Refrigerate and chill. Store in an airtight container in the refrigerator for at least 1 hour to let it chill.