Let's see...
A sub jumps to mind. I don't know where they found him, I am baffled how he managed to get into the school, but he inept in every facet of teaching. It's been a while, I was about 12 when he walked into the classroom, but I'll try to recall the events of that terrifying lesson.
He was a middle-aged man of middle eastern descent, for whom it was clear English wasn't his first language. He dismissed the lesson plan that had been left, and began just lecturing about the galaxy. I'm unsure to this day what exactly he was talking about, but it ranged from quarks to just abstract bits of information about astronomy. We were 12, did I mention that? He just rambled on and on... when he was "teaching" that is. I've yet to mention the fact he came in and was instantly hostile. Everyone pissed him off, and woe betide you if you so much as attempted to ask a question. By the end of the lesson he had threatened to kill us, otherwise harm us, and had chased at least one person out of the class punching him in the back, screaming "Never come back here again". Upon leaving he issued us ridiculously complex assignments, seemingly under the impression, this was his class (which would explain the complete lack of context from the rambling).
The guy who got chased out had it coming for so long, he was a dick, but still, this was a teacher and he was a 12 year old ****.
He was by far the most extremely incapable teacher I've had, but I've had others who were poor for other reasons.
Nearly every maths tutor I had, bar two, loathed me. I was an alright student, I wasn't disruptive or rude, and I got decent results and handed stuff in more often than not. So the abject hatred I inspired from at least three of them was just baffling. One in particular was truly one of the most unhappy, spiteful and bitter women I've ever met, and because of this, she had absolutely no idea how to get receptive students, or even interact with anyone who wasn't twisted and hateful. Thus, when idiots disrupted the class, nothing occurred teaching wise.
In fact, there was a more apt maths teacher I had, who I got along with better, and he could teach... so long as everyone was attentive and quiet. Needless to say, it was secondary school, that never happened, so I actually experienced very little learning in that room. He would just roar at everything, and that made the disruptors laugh, and he did not get it wasn't working. Le sigh.
I had a Classics teacher that "wasn't convinced by" evolution, didn't know the Fates weren't only a metaphor in Greek mythology, and often just repeated what had been read, rather than constructing on and exploring it. She was fairly annoying.
I also had a mad zealously overbearing women for English Language, who was certain I'd fail if I didn't attend extra classes. I got an A. She could teach, she just didn't have much likeability at all, she made it very hard to connect with her, her sense of humour was absolutely dead, and she thought what she taught needed a lot more depth than it did. She clearly wanted to be teaching at degree level, but couldn't, so subject the next step down to the grueling intensity that would come with end stage degree study.
In retrospect, I've had some teachers and lecturers so awesome that they completely overshadow most of the banal or inept ones, so really I've been very fortunate ^_^
