Bring a large pot of lightly salted water to a boil. Add the macaroni and cook until tender, about 8 minutes.
Drain the cooked macaroni and rinse under cold water until chilled; drain well.
In a large bowl, whisk together the mayonnaise, white vinegar, sugar, Dijon mustard, salt, and black pepper until smooth.
Add the chopped red onion, chopped celery, chopped green bell pepper, and the cooled macaroni to the bowl. Stir until everything is evenly coated.
Cover and refrigerate for at least 4 hours, preferably overnight, before serving to allow flavors to meld.