I always thought ketchup on a hot dog was barbaric. Ketchup on burgers, mustard on dogs. Until I discovered Hardees put mustard on burgers. So my theory out the window. To each his own.
The ultimate dog out in Arizona is the Sonoma dog. It has every condiment under the sun. Ketchup, mustard, cheese, bacon, tomatoes,, mayo, kraut, and the kitchen sink. And somewhere under all that is a hot dog.