I agree with Don, it’s not just guitarists, they exist everywhere. I have been fortunate, in that I have never had a guitar teacher who would show off. My first teacher was an amazing player, but I’d known him for years before I heard him do anything other than illustrate what he was trying to teach, and that was only because he was showing me a new amp he had bought, and why it was good. He was confident enough in his own abilities to never have to show off.
There was a great story about him from the early 80’s which I only found out about recently. He used to go and try guitars for pupils to make sure they were OK. He regularly did this at A1 Music in Manchester, because at the time they were one of the few shops in the North West doing top end rawk guitars. There was a sales ‘assistant’ who used to show off in front of the tutor before handing over the guitar. The tutor would check the neck, finish and fit and strum a few chords without being plugged in. He did this time after time for different pupils….never did anything more than strum chords.
One day the assistant must have pissed him off, because he plugged in, played Eruption note perfect behind his head, then handed the guitar back to the assistant.
The assistant stopped showing off, and the tutor went back to checking the neck, finish and fit and strumimg a few chords without being plugged in ;-)