I had a Math Teacher like the one you describe back in the 60’s.
He taught Calculus that you had to take as part of the Core Curriculum in freshman year . I went to every class but , couldn’t understand any problem he lectured on .
Plus , he chain smoked incessantly in Class.
I flunked the class and had to take it and 2nd Semester Math in Summer School with a different teacher I got 2 B’s
Then in my last Semester of Senior year , I had 1 last Math class to take . Guess which Professor I got ? My freshman Math teacher again .
The Gods were not kind !
Same result , except this time , most of the Class didn’t understand any of his lectures . 75 percent of a large class were failing , including me again .
The Class essentially mutinied and the Teacher finally says “ If no one goes to the Deans and complains , I won’t fail anyone .” Everyone signed on and instead of failing , the 75 percent all got D’s. It hurt my grade point average but , I wouldn’t have graduated on time , if I had failed .
He still smoked like a chimney in class though .
I often wondered why the University didn’t dismiss him ? He was terrible .