At most singing session/jam sessions that I've attended, if somebody sings a song that is "not working", the only ones who would get upset or rude (like talking over the singer) are the ones that were rude when they came in the door. One song "not working" is not the end of the world, and should not be a tragedy for any session that's worthwhile anyway. If a song itself (and its singer) is rude or inappropriate, like the nursing song mentioned above, hopefully that can be taken care of without a confrontation, but that's different from one that you just might not happen to admire the quality of. Unless you're in charge or paid to hear a specified list of songs, it's none of your (or my) business just because somebody's song is "not working".

I am continually dismayed at how many people of all ages never learned any manners (today called social skills) at all, to the point that the whole idea of being tolerant or kind or respectful to others seems other-worldly to them.

Chet