Yes, sitting opposite or a few seats away from a "musical" friend or partner is always a good move as Trish has observed. Then the MC can't accuse you of "collaborating"

Especially so for tune players. If you are seen to "join in", then some hosts will assume or argue that you've "had your tune".

I've also noticed that if you decide to "sit out" when asked the first time because you aren't quite ready, then you are unlikely to get asked again in many places.    :-((

Now one of my biggest gripes.

Singers and other instrumentalists who don't listen or give tune players the same order as singers, story tellers etc. This is understandable in a regular pub session but there is no excuse in an organised "Come All Ye", "Singaround" or "Round the room session" scenario.

@Flora G.... Re Norwegian and Gaelic tunes etc etc

" its not that they are unwelcome - just hard to listen to and even harder to join in with. Me - I really like them but I keep them for home playing."

The discussion is about the more organised session/singaround. So, you don't have to "join in"(It may not always be welcome, anyway) and it is more about listening.

Individual set instrumental pieces and many songs may indeed be "hard to listen to" but that is what is usually expected. Of course, many songs and tunes are ideal for "joining in" and most performers will welcome this. However, less well known and more serious pieces are usually better left alone.