Because I write my own material,I take it as a compliment when others join in on the chorus. If I see people looking unsure , mouthing the words I generally give an encouraging nod. On the issue of other musos talking over a performance , I am in agreement with uncle tone, though have never downed tools and left. I have often found that sometimes the offenders do respect what you do, despite the bad manners, and if that is the ethos of the club I am inclined to go with it if at least some are trying to listen !