Chop bacon and cook it in a large nonstick pan. Remove bacon and set aside.
Discard all but 2 tablespoons bacon grease. Add onion to bacon grease left in pan and cook until soft.
In a medium bowl, stir together ketchup, brown sugar, BBQ sauce, Worcestershire sauce, salt, pepper, and cayenne pepper.
Add green beans to a lightly greased 4 to 6 quart crock pot.
Add onions along with any bacon grease left in pan to crock pot.
Pour ketchup mixture on top and stir in.
Sprinkle bacon on top. Cover crock pot and cook on LOW for 4 to 5 hours.