When I was very new to lecturing, I stopped a lecture to ask a student to stop eating. Food wasn't allowed in the lecture hall, but my problem (and I said this, quite nicely and calmly) was that it was rustling and as he was about ten feet from me, I was finding the noise distracting. A few minutes later I had to ask again.
Amongst the various consequences of this (including an email from my head of department which, frankly, scared me because I was so new to it all), was getting an 'explanation' email from the student in which he told me he had, in his previous job, been in the army and therefore knew all about guns and killing people.
Try imagining how I felt for a few weeks.
I really hate student satisfaction forms. I usually get high ratings (I really care about my lectures and, honestly, they are good, and most students say they are interesting). But there are always some students whose comments are things like 'boring, I don't want to hear about [course content central to the degree they chose]' or comments on my clothing. Or, my personal favourite, students who cannot distinguish between my views and the views of the late medieval societies I'm discussing, and conclude I am homophobic, sexist or anti-Semitic.
I think with all of these kinds of students, you do learn to tune it out, but it is depressing.
My students are generally absolutely lovely, but the very few bad ones really get to me at times.