Stir tomato sauce, diced tomatoes, onion, cumin, cayenne pepper, and black pepper together in a large pot over medium heat; keep at a simmer as you prepare the meats.
Place the bacon in a large skillet and cook over medium-high heat, turning occasionally, until crisp, about 10 minutes. Keep the skillet on heat while transferring bacon to a plate lined with paper towel to drain. Crumble bacon and stir into the tomato mixture.
Cook and stir sausage in the bacon drippings until completely browned, 5 to 7 minutes; drain and discard grease. Stir sausage into the tomato mixture. Return skillet to medium-high heat.
Cook and stir beef in the hot skillet until browned and crumbly, 5 to 7 minutes; drain and discard grease. Stir beef into the tomato mixture.
Stir barbeque sauce and chili powder into the tomato mixture; adjust any seasonings to your preference. Add kidney beans and chocolate to the mixture; cook and stir until the chocolate is melted, 1 to 2 minutes.
Pour Irish stout beer into the pot and stir. Bring the mixture to a simmer and cook, stirring occasionally, until the flavors are well integrated with one another, about 1 hour.
Stir masa flour into the chili until smooth. Bring the chili again to a simmer; cook and stir until thickened, about 15 minutes.