The worst performance I ever saw was at my local folk club, the paid 'artist' was a man called Tomas Lynch.
I thought he was bloody awful, I had never heard of him, and so I thought I might as well and go see what he's like. Bloody crap, he sang three well known songs but to different tunes so that you couldn't sing along with him, and then he played his Irish pipes, and he had the drones on a tape/cd. so he wasn't even playing them properly.
He was just awful, I tell you I had a better time in the house with toothache. in other words just crap.