Just before serving, shred lettuce with a knife to make about 4 cups. In large skillet, fry bacon until crisp. Add vinegar, heat through. Remove skillet from heat; add lettuce and onion. Season with salt, pepper and sugar. Toss 1 to 2 minutes until lettuce is wilted.
This is a real old-timer in our family. It took us a while to remember how to do it. We just did it by heart.