I haven't suffered from this problem too much luckily TtR despite gigging up to three times a week in the past. On the rare occasion it has happened, for instance someone telling me in some pompous or unpleasant way that I'm playing a part wrong or using the wrong chords, or that I can't sing or play a particular song because I'm not from that city or country or whatever, I tend not to take much notice and certainly never lose my cool. If anything, these people just make themselves look bad without any help. If, on the other hand, someone suggests an improvement or alternative in a constructive and friendly way I'll always listen and often will take up the suggestion. I don't think you're ever too old to learn even sometimes from a beginner.

Peace

moo