Place the bacon and oil in a large saucepan, add ½ cup water and bring to a simmer over medium-high heat, then cook until the water is evaporated and the bacon is crisp and well rendered, about 10 minutes.
Add the garlic and pepper flakes and cook, stirring, until fragrant, about 30 seconds.
Add the chicken stock and scrape up any browned bits from the bottom of the pan.
Add the beans, 2 tbsp of the vinegar and the sugar, reduce the heat to medium low, cover and cook stirring occasionally until the beans are completely soft and cooked through, about 1 hour.
Add water as necessary if the pan begins to dry out and the beans start to sizzle.
Stir in the remaining 2 tbsp vinegar, season to taste with salt and pepper, and serve.