Slice the whole onion width-wise, to create thin circle slices. Place onion rings into a large bowl and pour buttermilk over it. Make sure onions are submerged. Cover the bowl and place in the refrigerator for about 30 minutes. (You can keep onions in buttermilk for a few hours if needed.)
Pour oil into a deep, large cooking pa and preheat it to 375° (or use a fryer). Cover a wire rack with a couple of sheets of paper towels.
Mix four, salt, and pepper in a large shallow bowl. Take sliced onions out of buttermilk and gently shake it off.
Throw onions in the flour, spread them out and toss in flour mixture.
Fry onion straws in heated oil until golden brown. Take out and spread them out on a paper towel to soak up excess oil.
Toss hot dogs in BBQ sauce in a large bowl.
Wrap each hot dog in uncooked bacon strips. Tucking in the ends of bacon so it doesn’t come apart.
Grill until bacon is crispy and hot dogs are cooked.
Place cooked hot dogs in warm buns and top them off with crispy onions. (You can add some more BBQ sauce to the buns if you wish.)