There are two bad teachers I have had that frustrated me simply because they didn't teach. I learned most of what I needed for those classes by reading the books and practicing on my own, until a real teacher took over.
I took a Radiology and Medical Assistant course at a trade school a couple years ago. The first teacher I had at this trade school I will call D. The second teacher I had there I will call A.
D tried to be everyone's friend instead of teacher. D never said anything when other students in the class would get up during tests to answer their phones. D would show us pictures of her vacations during class time and make us play silly little "get to know your classmates!" games that I could have cared less about, but I would have caused myself serious injury trying it.
I was 28 when I started this course. I realize that most of the other students were fresh out of high school, but I had been in the work force for several years by then, and I was going to school again to find a better job and change my future. I was paying for this schooling myself, and I took it seriously. A lot of those other students used class time as social hour, and D never said anything to stop them.
A, though, A was worse. I transferred from the morning class to the evening class to get away from D's class, and into A's. A was even worse about being everyone's buddy than D. A was also much cruder and inappropriate during class. A let the students get away with anything, and all he ever told us was what would be on the test so we could study for it. Well, those that were so inclined to study, anyway.
There came a point when another teacher, L, that had been hired for the school came into the class to watch A "teach" us. I remember A standing up at the whiteboard, writing down notes for us to copy, trying to behave like a real teacher, and getting angry when some of the more…well, let's call them "outspoken" students that were used to be able to play around with A during class wouldn't cooperate with the new situation. They couldn't adjust to A when A tried to be serious. At one point L actually asked A, "How do they learn?" I told L that I just read the book.
Soon after this, A left the classroom, but I don't remember why, and L took over, writing the notes down for us to copy and explaining the reasons behind the information. L became my hero. I liked L from the beginning, even though most of the other students did not. A eventually quit entirely and L became our teacher, which made me happy. I learned a lot from L, way more than D or A could ever have taught me, and I'm glad to have had the chance to learn from L.