The thing is Andy, people who feel that it is important to let everyone know what they don't like have completely worn me out.
Some how or another, when the set is over, they manage to push ahead of the folks who want to say, "Thank you, that was my mother's favorite song" and tell you that you played it in D when it should have been G, or that you shouldn't have sung "Good King Wenceslaus" because is not a Christmas song, and is about "The Feast of Stephen", or that you were wrong to play a "piano blues" on your guitar, that I either should or shouldn't have played something by the Rolling Stones, or that it is immoral to play Maj7th chords.
And yes, they are entitled to their opinion, and yes, because I am the performer, I am obliged to smile and listen politely, and even to apologize. And yes, I shouldn't let that stuff get to me, and I usually don't. Over time though, you don't forget.
At some point, I remembered that customer service axiom that for every person whose complaint you receive, their are ten more who don't say anything. Given that I often played in coffeehouses or such places where a good audience often numbered 20-30,it came to me that it wasn't worth going out anymore;-)
Anyway, Andy, you'll be glad to know that you will never see my tuner on my guitar, or even my guitar, because I decline all invitations to perform. You're welcome to try your hand at it, though, and if I happen to hear you, I'll be only to glad to correct your thumb placement.