Cook macaroni according to package directions.
Save 1/2 cup of pasta water then drain the rest of the water and place macaroni and 1/2 cup of pasta water into a large bowl.
While macaroni is still hot, pour in vinegar, carrots and onion. Toss together until combined. Refrigerate for 15 minutes, or until cooled.
In a separate, smaller bowl, whisk together mayo, milk, and sugar. Fold mayo mixture into the macaroni until all the noodles are evenly coated. Add in celery and season with salt and pepper to taste.