Bring a large pot of salted water to boil, and then cook the macaroni until tender, about 10 minutes.
Drain and rinse under cold water, and then transfer the macaroni to a large bowl and chill in the fridge for a few minutes.
To make the dressing, mix together the mayo, vinegar, salt, pepper, and sugar. Add enough of the milk that the dressing is loose enough to coat the macaroni well.
Take the macaroni out of the fridge and add the pickle relish, pimentos, and chives to the bowl. Pour over about ¾ of your salad dressing and toss it all together. If the salad seems a little dry, add more dressing until you reach your desired level of creaminess.
Chill your macaroni salad for at least two hours before serving.