Looks like the newest burger for the "manly man" (as described in this commercial's title, "Beef 2012 Manly Man Campaign") at McDonald's in China features two beef patties, bacon, and...a hefty glob of mashed potatoes? The commercial starts by calling their beef patty "good," then the bacon "better," and finally, the mashed potato "best." Knowing how tasty McDonald's beef patties are, this may very well be the correct order of ingredient deliciousness.
Poking around the Internet hasn't shown the mashed potatoes-in-a-burger combo to be widespread, but here are some examples: this burger topped with mashed potatoes and bacon, this burger stuffed with mashed potatoes and (turkey) bacon, and Burger King's Loaded Steakhouse Burger topped with mashed potatoes, along with bacon.
What do you think of mashed potatoes on burgers?