Boil the potatoes, and when nearly done, sauté the bacon so it will be ready at the same time. Peel the potatoes at once and slice into a warm bowl. When the bacon is crisp, break it into small pieces. Add to the potatoes, along with the onion. Add the vinegar, salt, and pepper to the bacon fat, and heat thoroughly. Add to the salad and toss well. Correct the seasoning, sprinkle with parsley, and serve hot.