I can't say that this situation is all that unusual. Parents, particularly parents who are stay-at-home, have way too much time on their hands and involve themselves up to their armpits in the lives of their children. I have worked at schools where parents arrive at the schoolgrounds at lunchtime, and hang around on campus until the end of the day. For several weeks, parents lined up against the windows of one of the classrooms and stared at their children in class for the hour and fifteen minutes from the end of lunch to the end of the day. This continued until the teacher posted artwork blocking the parents view into the classroom from those windows. The parents promptly complained to the principal, and the teacher was ordered to take them down. That teacher (and almost every other teacher at the school) refuses to teach in that exposed classroom.
I've been the subject of ridiculous complaints also. I was too hard on a kid when I separated him for calling one of the girls a "cheating dog" (for using a calculator during a maths activity where I had explicitly allowed the class to use calculators). I take the roll at the wrong time of the day. I set too much homework (and, conversely, I don't set enough homework; a complaint made by the same parent). I don't hand notes out (I prefer to lay out the notes at the front of the class, and the kids are meant to pick them up as they leave). I don't insist that someone's little baby (senior elementary student) wear a raincoat if it looks rainy outside, and I don't help that student to put that raincoat on. I drink Ginger Beer which comes in a bottle that looks like it's a bottle of real beer (that it isn't is beside the point also, because Ginger Beer has the word "beer" in it, and therefore, I'm setting a poor example to students). I advocate the use of facebook (which is actually Edmodo, which, I'll admit, does look a lot like facebook, but isn't). I am biased against or for particular students because I select them for debate teams, public speaking competitions or sport (sometimes I am still biased against particular students when I'm not involved at all in the selection or non-selection of them for various opportunities). On and on and on. Most of these complaints are, as other commenters have noted, housewives with too much time on their hands. I can't tell you how much I appreciate that I have had a good principal who, for the most part, only wastes a little bit of her and my time every so often to investigate and respond to these claims.
That being said, I think that teachers and educational institutions have to acknowledge some responsibility in allowing this to happen. We encourage a dialogue between parents and teachers on an equal level, and we don't say all that much when unqualified pundits make educational claims that are simply wrong. Anyone, no matter how unqualified, will happily make claims about education and expect that those claims have equal footing with qualified and experienced teachers. In addition to my teaching degree, I have an undergraduate degree, a masters, and a graduate certificate in my area of educational specialisation. I have over 10 years experience in teaching, including 3 years teaching teachers how to teach at a university level, and 6 years as a recognised expert in working with a particular area of education. And, yet, I have to constantly respond to e-mails, that are sometimes less than polite, demanding to know why I do some "maths stuff" while I'm teaching science, for example.
Educators have to put themselves forward as experts, because they are, and this is the only way to change the prevailing culture. How many times do you hear people questioning (and expecting to be taken seriously) the moment to moment decisions of doctors? Lawyers? Even unqualified mechanics are held in higher esteem than teacher. The reason why is that these professions put themselves forward as experts, and they allow questioning (or a "second opinion") only from other experts. This is how teachers should be.
