In small bowl, combine vinegar, mustard, catsup, paprika, salt and pepper. Slowly add oil, beating constantly with electric mixer. Stir in celery and onions. Pour sauce over shrimp. Marinate 4 to 5 hours in refrigerator. Halve and peel avocados. Lift shrimp out of sauce and arrange on each avocado half. Pass sauce. Good served with chilled asparagus, carrot strips, sliced beets and hard-cooked eggs. This is a good luncheon dish and also can be served with toothpicks as an appetizer. Mrs. Neel Garland. From "River Road Recipes, II", published by The Junior League of Baton Rouge, Inc., 1980.