Boil macaroni in salted water until tender
Drain and rinse with cold water
Let macaroni cool completely
Chop celery, onion, and any other desired vegetables
In a bowl, mix mayonnaise, vinegar or lemon juice, mustard, salt, and pepper
Add cooled macaroni to the bowl
Add chopped vegetables and any optional ingredients like eggs, pickles, or ham
Toss everything until evenly coated
Taste and adjust seasoning if needed
Chill in the refrigerator before serving