When I was growing up this was mixed in our house every other day in the summer, either by my mother of grandmother. I guess they didn't know you could make it ahead and store it in a cool dark place for up to two weeks. It was used on the cucumber and onion salads, with no oil added, and on tender lettuces with the oil to coat the leafy greens. Of course there was no recipe, so I got this one from one of my favorite cook books The Gift of Southern Cooking.
Makes about 1/3 cup
The Gift of Southern Cooking
2 tablespoons granulated sugar
1 teaspoon salt
1/3 teaspoon freshly ground black pepper
1/4 cup cider vinegar
2 tablespoons peanut or vegetable oil
Put the sugar, salt, pepper, and vinegar in a clean pint jar. Screw lid on tight, and shake well until the sugar and salt are dissolved. Add the oil, and shake vigorously to emulsify. If made ahead and stored be sure to shake well again before using.