Kentucky Fried Chicken is bringing back a legendary fan-favorite after nearly a decade. The “KFC Double Down” is coming back for a limited time, as of March 6. The gut-bomb uses two fried chicken filets to sandwich two slices of cheese, bacon and a choice of mayo or spice sauce. The Double Down made its debut in 2010 and sold more than 10 million sandwiches. It also “generated more buzz than any test market item in KFC history.” What is the best fast-food menu item ever? What's the worst?