Soak 1/4 cup minced red onion in cold water, 10 minutes; drain. Cook 8 ounces elbow macaroni as the label directs; drain and rinse under cold water. Toss the macaroni, onion, 1 chopped celery stalk, 1 chopped hard-cooked egg, 1/3 cup mayonnaise, a pinch of cayenne pepper, 1 tablespoon each olive oil and white wine vinegar, and 3 tablespoons chopped parsley. Season with salt and pepper.