Chop your bacon into bite-sized pieces and add them to a large skillet over medium heat. Cook until the bacon is crispy and the fat has rendered into the pan, about 8 to 10 minutes.

Transfer the cooked bacon to a paper towel-lined plate, leaving the fat in the skillet. Add your ground beef to the hot bacon fat and cook over medium-high heat, breaking it up with a spoon as it browns, about 5 to 7 minutes.

Add your diced onion to the skillet with the beef and bacon fat. Stir and cook for 3 to 4 minutes until the onion softens and becomes translucent.

Drain and rinse the pinto beans and kidney beans. In a large slow cooker or mixing bowl, combine all four types of beans, along with the cooked bacon, beef, and onion mixture.

In a separate bowl, whisk together the brown sugar, ketchup, barbecue sauce, apple cider vinegar, Worcestershire sauce, yellow mustard, smoked paprika, garlic powder, black pepper, and cayenne pepper.

Pour the sauce over the bean and meat mixture in your slow cooker or baking dish and stir thoroughly.

Cover your slow cooker and cook on low for 2 to 3 hours, stirring occasionally.

About 10 minutes before serving, remove the lid and stir the beans. Taste and adjust seasoning if needed.