Cook elbow macaroni according to package directions. Drain and rinse under cold water.
In a large pot, place water, vinegar and 2 TB of Old Bay Seasoning to a boil - add shrimp - cover and cook 3 - 5 minutes or until shrimp turns pink. Remove shrimp from liquid and let shrimp cool. When cooled cut large shrimp in thirds or small shrimp cut in half. (You can cook these the evening before and let cool in the refrigerator overnight)
In a large bowl mix the mayo, celery, cucumber, onion, 2 tsp. Old Bay seasoning, celery seed, roasted red pepper, and then add shrimp. Refrigerate for a couple of hours before serving.