That was bold of you, Kendall!!! Cecil Sharpe House!
The most 'unexpected' song I've seen done at a proper gig in a Folk Club (as opposed to just folks 'messing about') was probably Dire Straits "Romeo & Juliet", with just one guy singing & accompanying himself on acoustic guitar. It worked too, as you might expect..it fits the 'idiom' even though the song itself, & its 'musical sources' arent necessarily what you would expect to hear in a folk setting.
'course, Mark Knopfler's 'folk' connection is fairly well understood, I think.