When I was in college decades ago, a friend of mine interrupted the rock background to urge someone to sing "Brennan on the Moor." Most of the guests seemed stunned that somebody was actually singing live and for free, unaccompanied, a song they'd never heard of with a catchy tune, an interesting story, and a rousing chorus. The singer was roundly congratualted.

That's the only time I can remember a singer performing essentially solo at a nonmusical party.