Bring a pot of salted water to a boil and cook your macaroni 1-2 minutes less than directed. Drain and run cool water over pasta. Put into a large bowl and add onion, carrot and green pepper. In a separate bowl wisk mayo with cider vinegar and add salt and pepper to taste. If it is too thick you can add a little water. Make sure dressing is to your liking. You can add more vinegar if you want or more mayo. Add to pasta bowl and stir well. Taste and adjust salt and pepper.
Let sit overnight so that the ingredients can blend together.