In a medium bowl, combine barbecue sauce, honey, grape jelly, minced garlic, and red pepper flakes (if using). Mix until smooth.
Place frozen meatballs into a crockpot and pour the sauce over the top. Stir until meatballs are evenly coated with the sauce.
Cook on high for 2-3 hours, or on low for 4-6 hours, until meatballs reach an internal temperature of 165˚F.
Optional: Sprinkle with chopped parsley before serving.