Bring 4 quarts of water to a boil in a large pot high heat. Add 1/4 cup of salt to the water and stir to dissolve. Carefully add the potatoes to the water and return to a boil.
Boil the potatoes for between 8 and 15 minutes, depending on what size you cut them. Beginning at 8 minutes, use tongs to extract a piece of potato and test for doneness. Do this until they are tender and easily pierced with a fork, knife, toothpick, or skewer.
Drain in a colander, then immediately return the potatoes to the pan.
Add vinegar and diced sweet onion to the pan and toss to distribute. Put a tight fitting lid on the pan and refrigerate to bring the potatoes to body temperature.
Stir in the mayonnaise, Dijon mustard, green onions, parsley, chopped hard-boiled eggs, and chopped, crispy bacon. Transfer to a serving bowl.
You can either garnish with the remaining bacon, hard-boiled egg, parsley, and green onion and serve warm, or cover and refrigerate to chill.
If you refrigerate it first, stir, and add a little extra mayonnaise if needed before garnishing and serving.