Richard Bridge.
I did a gig at a folk club in london,I did a version of a traditional song,somebody in the audience decided to join in,but they were using different chords to me.
no it wasnt ok,its good manners to ask[IAM NOT TALKING ABOUT JOINING IN CHORUSES]but deciding to accompany someone who doesnt need any accompaniment,or already has their own perfectly good accompaniment.
I dont know if it is a full moon,but you dont seem to take it in to your cranium ,that I have never[as an organiser] not allowed a floor singer to sing,but I repeat, an organiser has that right if they wish to do so,they are organising/financing the club.,whether I wish to exercise that right is a different matter[I never did ].