Brown the ground beef. In a large skillet, cook the ground beef over medium heat, breaking it into very small pieces as it cooks. Drain the excess grease.
Add the ingredients. Transfer the cooked ground beef to your crockpot. Add the brown sugar, mustard, ketchup, tomato paste, Worcestershire sauce, minced garlic, salt, pepper, red pepper flakes, and water.
Stir everything together. Mix well until the beef is coated with the sauce and the ingredients are evenly combined.
Cook in the crockpot. Cover and cook on low for 2–3 hours, stirring well before serving. Make sure the beef mixture reaches a safe temperature of 160°F (71°C).
Serve and enjoy. Spoon the sloppy joe mixture onto hamburger buns or slices of bread. Serve with chips, French fries, and pickles.