1Put the potatoes in a medium saucepan and cover with cold water. Bring to a boil, then reduce the heat to medium and cook until fork-tender, about 15 minutes. Meanwhile, sauté the bacon in a skillet over low heat until crispy, about 12 minutes. Drain on paper towels.
2Put the eggs in a small saucepan and cover with cold water. Bring to a boil, then remove from the heat, cover and let stand 6 minutes. Drain and run under cold water to cool; peel and chop.
3Drain the potatoes (do not rinse), transfer to a baking sheet and let cool 6 to 8 minutes. In a small bowl, combine the vinegar, Greek yogurt, mustard, red onion, scallions, sugar, and salt and pepper to taste. Transfer the potatoes to a large bowl and add the bacon, bacon grease and hard-cooked eggs; fold in the yogurt mixture. Serve at room temperature.