Another vote for Canalwheeler's post on 23.10. I go to a number of different sessions, but one which contains many of the features that are anathema to some: people using crib sheets, singing off key, changing key repeatedly mid-song, timing idiosyncrasies etc. but yet it is a lovely friendly club and we put up with each other's imperfections and everyone supports each other. It is not a concert, after all!
I have very rarely had a private word with someone, twice because there had been a change of a key word from the original song which completely altered or destroyed the meaning of the song: they had "got the words off the internet", of course!
And once when the singer had the verse and chorus tunes in the wrong places, which kind of threw anyone trying to join in the chorus: "most people usually sing it this way" was my approach, rather than "you've got that all wrong". He thanked me several weeks later, and certainly was not offended.