@newpedals Re that unsolicited advice that teacher gave you at your gig... I've learned in most situations like that, people mean well. Even when I don't like the way someone gave me criticism, I try to ignore that part, and hear what they're trying to tell me.
I've been out to clubs with musician buddies of mine, in which we all agreed about some aspect of the band's sound, maybe something like the guitarist not cutting through the mix. We all assumed the guitarist wasn't aware of it, but we said nothing, even though we thought some feedback would surely help them sound better. Why? Because none of us wanted to be "that guy."
I'm actually the opposite: I
want feedback, good
or bad. Especially bad, because those are things that I'm most likely not aware of, and usually, no one is willing to say anything. If it happens to be something I
am aware of, and I disagree with, then I simply ignore it. And say "Thank you."
Back when I started out, whenever I took a solo, I would open my mouth really wide. I can only imagine how stupid I looked.

Finally our drummer told me. And told me I'd been doing it for some time. I was like, "WHY DIDN'T YOU
TELL ME?"
They didn't want to hurt my feelings!

Ok, but allowing me to continue looking like a fool was the better choice?
So even if someone doesn't know you, and offers you some advice, even if they deliver it in a less-than-tactful manner, first off, it took guts to even say anything. And second, they were most likely just trying to help.
And at the end of the day, what musician out there doesn't honestly want other musicians to sound as good as they can? I believe it's also part of the reason we're all here too.