In a large pot boil potatoes in salted water until softened but still firm, where you can pierce it easily with a fork. about 20-25 minutes. Drain the potatoes and set aside until cool.
To make the dressing: In a mixing bowl whisk together the mayonnaise, mustard, and vinegar. Then stir in in the celery, onion, pimentos, pickle relish, and chives. Season with salt and pepper. Cover and set in the fridge until potatoes are ready.
When the potatoes are cool enough to touch peel the skins if you want then chop the potatoes into ½ inch pieces. When the potatoes reach room temperature, fold in the mayonnaise mixture until evenly coated. Season with salt and pepper and chill in the refrigerator for at least an hour. Lasts for a week in the fridge.