My own critic wasn't an organiser, just a fellow singer.

Turning it round: how would you feel? You've learnt a song, worked on it, practised it, worked out where to pitch it, thought about which bits to ornament or not, where to speed it up or slow it down, etc, etc. You take it to a singaround where you sing it just as well as you did at home, and it goes down well. You feel pretty good about it. Then the (unsolicited) helpful comment - "lovely song, such a shame you messed up that bit..." How would you react?

My own reaction was to assume my critic was 100% right, which must mean that I was 100% wrong and couldn't trust my own ear, which in turn must mean I'd been unwittingly embarrassing myself & everyone else for the last ten years of singarounds and floor spots. It didn't exactly make my evening. On reflection I think I should have reacted more like Will's Duck Dancer approximator.