My old Junior School maths teacher, Mr. Wright.
Why was he bad? He insulted every student he had. Not as in the jokey-insult way teachers can be awesome for, he just generally hated us all with a passion and wasn't ashamed of showing his contempt. He used to just pick out one aspect of us and torture us for it endlessly.
For example, the 'bully' of the class would get insulted relentlessly for apparently being stupid on caveman levels. The most popular girl was ridiculed for being a slut-in-the-making (this girl was in Year 5 at the time!) and me? Well I was the most feminine guy there, so I got called homophobic slurs on an almost-daily basis.
Yeah, I hated his classes.
Then were was Mr. Burke in Secondary School. He had a massive amount of dislike for anyone who wasn't obsessed with sports (he was a P.E teacher) and wasn't afraid to hide it. He openly praised everyone who did well in sporting activities, but people who didn't care about 'real sports' (which in his mind were football, rugby and basketball mainly) were dumb little freaks who weren't going to get anywhere in life.
Then there was Mrs. Jacobs...the Sex Education teacher.
She wasn't BAD, exactly, she just had a sense of humour that really wasn't appropriate. She, like Mr. Wright, picked up on my feminine qualities and repeatedly made references to the fact that I might be gay. That's...not fun, when you're in a class filled with bullies who already hate you. Arming them with that information just wasn't cool.
In Secondary School there were a few.
Ms. Hail was just a cold hard ***** of epic proportions
Mr. Jenkins was a smug asshole who assumed 'if I can do it, there's no reason you can't' without factoring in that we were students and he was a trained professional.
The ultimate epitomy of horrific teachers, however, was Mr. Mere. At least in my opinion he is.
Basically, I had him as an art teacher for all 5 years and he spent that entire 5 years making homophobic slurs against me whenever possible, and encouraging anyone else who did the same.
I fucking hated him...