I would say LOL, but the accordionist sounds a right a**hole, as I believe our American friends would say (correct me if I'm wrong, guys). I'm fairly gobsmacked at the arrogant behaviour of this person, as described above.

Presumably the accordionist thought "Shoals of Herring" was "his" song, and objected to this interloper. Of course that's no excuse.

I've occasionally been "beaten to the punch" in a singaround when I've had a song lined up. I'd just shrug my shoulders and do something else - there are plenty of soungs to choose from - and I'd probably mention it jokingly to the "usurper" afterwards ("Yer b*gg*r, yer nicked me song") :)

I will only join in and accompany another singer (or musician) if I can play it in the same key as them (as a guitarist I can use a capo anyway, so it's rarely a problem) - I wouldn't dream of asking them to change key to suit me (of course I'll only do so if I'm able to play it properly in the first place, and if the person is happy for others to join in). When I sing a song I sing it in the right key for my own voice, which is often different from the 'official' written key. If I didn't do this, I'd not be able to reach all the low or high notes. I wouldn't want to change it for anyone else and I wouldn't expect anyone to ask me to.

Likewise if I want to join in vocally I will if necessary sing in harmony to suit my voice (and I hope, the song) - again I wouldn't dream of asking the lead vocalist to change to suit me.