The worst teacher that I had was my junior high school science teacher. He would just stand their and yell while the students ran wild AND he was also my mothers worst teacher 30 years earlier! The poor guy went through that everyday for at least 30 years!
I was still very good in science (relative to my abilities in other classes) and I got A's in science even the year after I had him.
To me teachers and school seem much less important that we assume that they are. See the work of Bryan Caplan.
BTW One of the other bad teachers that I had my mother had also had. She was bad in that she spent half the day in the teachers lounge but the students feared her so their was not much chaos.