Mix the amount of mayonnaise you think you will want with sufficient vinegar to make a smooth, slight runny consistency. Mix all dry ingredients together, and add sufficient of the mayonnaise mixture until it all 'hangs together' (Ricky's words!). Place potato salad mixture in a mound on a serving dish and surround with halved hard-boiled eggs. Drizzle a little extra mayonnaise mixture over the eggs and garnish with parsley.