Bring a medium pot of water to a boil (just enough water to hold pasta and shrimp). Salt generously and add 1 tablespoon old bay. Then stir in the pasta noodles. Cook until tender but firm, 6-7 minutes.
Turn off the heat, add the shrimp and stir until brightly colored and just cooked through, 2 minutes. Drain (don’t rinse!) and leave in the colander to cool for 5 minutes. Shake the strainer periodically to help drain.
In a large bowl, whisk together mayo, milk, grated garlic, dijon, remaining Old Bay, lemon juice and zest, dill and black pepper until well combined.
Add the cooked macaroni, shrimp, diced celery, scallions and red pepper to the bowl. Stir until coated. Cover and refrigerate until serving. (Flavors will build as the salad sits). Taste and add more Old Bay, lemon, salt or pepper before serving.
If the pasta has absorbed too much of the dressing, whisk a few tablespoons of mayo and milk together and stir into the pasta. Garnish with more fresh dill.
