Had two bad teachers, although bad in a different way.
One was a young, inexperienced teacher that I feel wasn't cut out for A level as he basically relied on textbooks too much and didnt know anything off the top of his head and was way too relaxed, he tried to be 'fun' and relatable to the class which just resulted in not much work being done.
My worst was my chemistry teacher, I despise her so much. She was incredibly sarcastic and mean, if you suggested something that was wrong she'd ridicule you infront of the whole class. She would talk so harshly about students that several occasions, someone in the class was reduced to tears. A few parents even complained because students were so unhappy.
I was really into chemistry at GCSE, with an A*, I even visited the royal society of chemistry and was all for getting a degree in it but I guess her teaching style didn't mesh with me, she was focused on making us like highlight notes and make a 'neat' work folder and that's not my style. So after a disappointing but decent grade in my first year, which was actually higher than most of my class she decided to predict my A2 grade to be even lower. She also gave me a pretty bad UCAS subject reference, all my other teachers basically saying I was a delight and her saying I didn't have the mindset to achieve. She broke my resolve through her comments and just general put-downs, I got to the point where I was scared to ask questions in lectures in fear of being mocked. The way she spoke to me made me avoid her. I basically sat in silence in my classes, head down. I remember once I was late to school due to my bus being late, and I decided to just sit out rather than face her because she'd like to make an 'example' of late students. She would throw a students 'bad' work on the floor, she basically told me to my face there was more chance of hell freezing over than me passing.
I don't blame her entirely for my failings in chemistry but I do feel she greatly impacted me more than academically, I was a bright-ish student who loved to ask questions and was engaged in my classes, but after her as a teacher I was so scared of mistakes and being ridiculed that I basically never hazard a guess unless I am sure to be correct. Even a few years on now, at university I feel she's changed my personality irreversibly, like I'm a lot more quiet, reserved and in fear of looking bad than I was before.
She is one of my main motivations to make a success of myself so I can prove her wrong.