My worst class by far was taught by a visiting professor who just did not give a damn and basically read from a textbook. He was gone after a semester. I suspect it was partly due to his horrid student reviews.

I also had a math class taught by a well meaning fresh professor. It was on the fast Fourier transform and related techniques leading to it. Great topic choice but very awkwardly and confusingly taught. It is actually hugely relevant to video compression and decompression.