The origin of "Dueling Banjos" is a bit of urban folkore I can address from personal knowledge (none of theis "I have it on good authority" crap).

Once upn a time, in the southern portion of New York City, a folkie named Izzie Young opened a shop called The Folklore Center. One day, in a fit of something or other, another folkie (Bob Pliskin, who happens to lurk the Mudcat) hung an odd thing in his window: A banjo, outfitted with a bayonet. And below it was a placard reading: one half of the only set of dueling banjos in existence.

A third folkie, of the bluegrass persuasion, named Eric Weissberg, was taken with this concept. And so, when Weissberg re-arranged an older Reno/Smiley tune called "Mocking Banjo" for a forthcoming movie called Deliverance, he called it Dueling Banjos.

So help me Hannah!