Prepare shrimp. Pat your cooked shrimp dry with a paper towel and then sprinkle with one teaspoon of the Old Bay seasoning and toss so that all of the shrimp is lightly coated.
Make the dressing. In a small bowl combine the mayonnaise, lemon juice, remaining Old Bay seasoning, sugar, salt, and pepper. Whisk together.
Combine ingredients. In a large bowl combine the cooked macaroni, cooked and seasoned shrimp, green onion, red bell pepper, celery, and red onion.