Place potatoes in a large saucepan and pour in enough water to cover them; set pan over high heat and bring to a boil. Reduce heat to medium and simmer until potatoes are fork-tender, about 20 minutes; drain. When potatoes are cool enough to handle, slice each into quarters.
Meanwhile, cook bacon in a hot skillet or in the microwave until crisp; drain on paper towels. Break bacon into small pieces.
Transfer potatoes to a large bowl; add bacon and scallions. Add mayonnaise, vinegar, parsley, salt and pepper; mix until blended. Yields about 3/4 cup per serving.