Pet hates are:

1 Anyone talking/playing a different tune.
2 Getting up to go to the loo just as someone starts a song -particularly bad if its the person who has just introduced them or is running the session
3. Session leader not doing their homework on guests - Ive seen a well known artist introduced as someone else.
4. Know it alls who, as soon as someone finishes a song or tune, begins to disect it or tell everyone present that it wasn't the original tune/words etc etc.
5. People who insist on trying to accompany a song they've never heard before, or when its obvious that the singer does not want accompaniment.
6. People who try and harmonize with every song they hear - it puts me off when I have difficulty singing in one key when someone is singing in another.

Overall, I believe that anyone -especially newcomers- who is brave enough to sing or play in public, deserves a minimum of respect from those present especially the more experienced people.