Its been a good long while since I waded into the Mudcat discussion boards, but here I am.

We all have our pet hates at sessions, one of mine is people who sit and tut at you for making a mistake when your accompanying someone. We do make mistakes sometimes us musicians.

My other main one is when you have made youself some room in the corner where you aren't going to hurt anyone (I'm a fiddle player) and someone pulls a stool from somewhere and sits right next to you, right in the "bow in the eye" position

But anyway, I digress.   We all have different opinions as to what is good etiquette, and I suppose it all come down to the club/venue. I personaaly think that common courtesy is the best plan. Keep the volume down where possible, and as for joining in, I make a point when Im singing of asking accompanists to wait until after the first verse, so I can set my key/tempo etc