Boil lightly salted water in large water pot. Pour the macaroni, and keep cooking it until it is soft, for 8 minutes. Drain it after rinsing it under some cold water.
Blend vinegar, mayonnaise, mustard, sugar, pepper, and salt in a large bowl. Pour celery, onion, carrot, green pepper, macaroni, and pimentos. Before serving, keep it refrigerated for 4 hours; you can even keep it for the whole night.