When I was a student, I would NEVER send my professors emails complaining that the exam was too hard, therefore the professor must not know how to teach. And yet here I am with an inbox full of rude emails about the same exact exam I've been giving for decades... telling me that I am bad at my job because the student didn't have high school pre-calc skills that they needed for their calculus class. The grade distribution is excellent -- maybe even high -- and I have years' worth of great reviews and comments from students and faculty alike. I have a stack of teaching awards and honors to boot, so I do know what I'm doing. 

Struggling with an exam and contacting the professor for help is good and encouraged, but this isn't what's happening here. Maybe one in ten of my students speaks to me like this. I've talked to a few of my colleagues and they have the same complaint. Is this because I've been teaching so long and have become hypersensitive or are the students actually getting worse? Has anyone conducted a study about this behavior?