Oh lets be honest, not all instructors are perfect. There certainly are some terrible ones around.
I've had two in my time, that I'd have prefered to avoid. Admittedly I've learnt something from both of them, but overall, there were not good for my flying.
One
insisted that I change the order of my downwind checks before he sign me off. Not because there was something wrong with my order, but because it was different from the order he did them, and as a result he couldn't easily check that I was actually doing them all. (He did agree that everything in my downwind checks were in his, just not the same order).
The other told me to stop running the trim wheel fully forward and fully back as part of my start up checks. He said that I should only check that it can be moved and a half roll forward and a half roll back was enough; otherwise I'm wearing it out
As Katamarino suggests, I just grinned and bared it, and afterwards did my own thing. I did learn at least one good thing from each of those two instructors, but overall, I would have prefered to avoid them (for plenty more reasons than above).
Pretty much all of the other instructors I've come across have been excellent, but it would be unfair to say that David could not have come across a plonker of one.