I'm another one saying students need to learn professional courtesy/email etiquette. Even mature students. I think it ought to be part of our job.
That said, I had my own issue with a student recently, who wrote an email that was (probably mistakenly) much, much ruder than they realised and much ruder than I should have to put up with. And I did write to them to explain that they needed to reassess their understanding of professional courtesy, because they would alienate people otherwise. I didn't try to make it sound snide or mean - just informative.
Oh God, this. On two recent occasions one an undergraduate, one a PhD student I've had two very rude emails, only to discover, when the two students in question came to see me at my request, that neither of them had consciously intended any rudeness at all. In one case, it was just a complete ignorance of how you write a normally polite email, and in the other, the student simply had a tin ear for tone (which as you can imagine is not the best qualification for someone studying literature). 
And, in terms of being challenged by the more lowly. An cautionary tale. A close relative of mine recently retired as Head of a large, prestigious University department. The relative (.being cautious here about details) had spent some years developing a ground breaking new piece of research which was presented at a conference of academics from around the world. When it was time for questions, the question, apparently, from the front row, from a 20 something, shot a fatal hole in my relative's research. Said relative remained as Head of department, kept the Professorship, but it was all based on work from years earlier.
Said relative then began referring to themselves as a teacher and focussed far more on nurturing talent and less on highlighting previous laurels.
Hamlets I don't think you can have understood your relative's story, or how academia works. No one credible, in any field, still less a professor, just bobs up at a conference with something that hasn't been multiply tested/discussed/evaluated elsewhere. Typically, a project big enough to have taken up several years of research time will have needed major funding, which means that even before the research is embarked upon, the viability of the research will have been assessed and peer-reviewed, often many times, by assessors for the funding bodies applied to. A single question from a brilliant doctoral student may have exposed a flaw, or asked a new and difficult question (which is what conferences are for, after all!) but it won't have fatally punctured any credible large-scale research project.
And are you actually suggesting that there's a mechanism for defrocking professors once their current research has been found wanting? Also, absolutely no one wants to be head of department, which is rather like amputating your own leg with a butter knife, only with a lot more bureaucracy.