Bring a large pot of salted water to boil (I usually add about a tablespoon of salt to the water, but you can skip this if you don’t want to add it). Add the macaroni and cook until just tender, about 8 minutes.
While the macaroni is cooking, mix together the mayo, vinegar, sugar, mustard, salt and pepper. Reserve 1-2 tablespoons.
Mix together macaroni, onion, celery and bell pepper and pour dressing over top, minus reserved. Mix well and chill at least four hours.
Prior to serving, add reserved dressing and stir.
