I tend to agree with you, Jim,However there have been a few occassions when someone spontaneously sings a harmony that is really good.
on the occassion,when I was guesting at a london folk club,and another concertina player, joined in playing a different chord progression,I was flabbergasted.
on the other hand I have no problem,with the club where the organiser makes bird /sheep calls,I am prepared for it,and try either not to include songs that feature birds/ sheep,or to turn it to my advantage as a performer by making a joke out of it,sometimes it pays to be easy going,and not lose the head.
organisers choose which guests to book,but guests are under no obligation to play any club ,that they dont fancy.
I can understand the guy pouring beer over someones head,but in the cool light of day it wasnt the best solution.