Two math teachers in my university.
The first was a professor of differential geometry who had been assigned a 100-level algebra/analytic geometry class-- basically between entry-level algebra and trig in terms of difficulty. He’d come to class and just sorta… wing it. And yell at students. Scream at them. In front of other students, in private, wherever. Before I’d found this out, I was in his class when he wrote some simple equation on the board-- something like nx/2 + ny/4 = n. “Okay, what do we do first?” I rose my hand-- “you could simplify by dividing through both sides by n,” which caused him to turn around in a rage, throw the chalk, and begin shouting that I needed to think before I opened my mouth, that I knew nothing of algebra-- and how’d I pass the prior algebra class since I was so obviously stupid-- and that my stupidity was sure to utterly befuddle the other nimrods in the class. Later that week, he approached me while I was outside studying, and was shaking with rage as he told me that I was worthless and should think about dropping out of school.
Thankfully, he was quite the fair grader on quizzes and tests, and I got a 4.0.
The second was a nice little lady from Poland who taught beginning abstract algebra/logic. Her method was to have us work in small groups, and make half of our grade in the class based on participation points, painstakingly making little hashmarks next to our names in a gradebook every time we went to the board to solve a problem we were all given. However, she had the tendency to begin snarking “Sit down! Sit down, you stupid! You know nothing!” if anyone made the tiniest error at the board… so eventually, in a class of 40 or so students, only three of us had the nerve to go up with any regularity. She was also oddly critical of non-essential language in our proof writing-- “don’t say ‘for all x in M,’ it confuse you, say ‘for every x’! See? See how sublime! Yes! Write it! Erase your ‘all,’ here let me write ‘every’ for you!”
She also really never taught us any abstract, logic, notation, or anything. Her advice on tackling a problem: “Oh, sometime I take days. Weeks. To think! Yes, to think of what problem say! And then I meditate, I sit on pillow and light incense! Math not always logical, math is mystical!” Rockin’, that’ll work on that one hour final exam.