Cook the bacon: Cook the bacon in a large skillet or Dutch oven over medium heat for 10 to 12 minutes, until almost crisp. Leave the drippings in the pot.
Soften the onion: Add the onion and sauté until translucent, about 7 to 8 minutes.
Add the garlic and herbs: Stir in the garlic and rosemary or thyme and sauté 1 more minute.
Add the broth and greens: Add the red pepper flakes, broth, greens, vinegar, sugar, ¼ teaspoon salt, and ¼ teaspoon pepper. Stir with a wooden spoon, scraping up any browned bits from the bottom of the pot.
Simmer and mash: Stir in the beans and bring the liquid to a boil. Turn the heat to low and simmer, mashing some of the beans against the side of the pot, until the liquid has reduced and thickened, 6 to 8 minutes.
Finish the greens: The greens should be wilted and slightly tender at this point. For softer greens, cover the pot and simmer gently until they reach the tenderness you like.
Taste and serve: Taste and season with additional salt and pepper if needed. Serve with cornbread.