Maybe manners are better here in S.Wales. Nobody has yet told me not to sing, or that I'm crap.
I sing unaccompanied, sometimes with a sheet of the words, sometimes without. Sometimes I sing with my eyes closed (reviewing the coming lines!).
If I have to leave the room to get a pint or two (it has been known to happen) I don't walk out on some newby, or during a song, I wait until a singer I know is being introduced, and who I know will not think it's a comment on his singing/playing ability.

Different strokes for different folks!