Mix sauce: whisk together BBQ sauce, brown sugar, apple cider vinegar, garlic powder, onion powder, paprika, salt, pepper, and red pepper flakes if using.
Add chicken: place chicken in the crockpot. Pour sauce over to coat all pieces.
Cook: cover and cook on low 6 to 7 hours or high 3 to 4 hours until chicken pulls apart easily.
Shred: remove chicken, shred with two forks. Return to crockpot and stir into sauce.
Thicken sauce (optional): ladle out 1 cup sauce, simmer 5 to 8 minutes, stir back in.
Serve: serve hot on buns, over rice, or as desired.