I get really irritated when teachers believe they have the right to demand I stop my sudoku and pay attention to the class.
To begin with, attending school is not optional. I am forced to do it. However, nobody has entitled them to actually have control over me, as long as my behavior is not detrimental to the integrity of the course.
Secondly, in many cases I already know more than they do (Mathematics, Computers, Music, Writing, etc), and they have nothing to offer me.
Lastly, IT IS 7 FREAKIN' HOURS PER DAY! I have calculated that I have wasted about 8500 hours at school since the first grade, and most of my knowledge, I have attained online. School is one of the most useless concepts in the world, especially when homeschooling is not an option (stupid Greek educational system).
Oh by the way, it is unconstitutional here, since it is a form of illegal arrest (forced attendance 7 hours a day, without my consent.).
Summing up, No, I do not care about your lesson, you are an idiot and have no right to "teach" me things that are incorrect ("sqrt(-1) does not exist"), and I will finish my sudoku.