In undergrad, I had the worst teacher I've ever had in my life. No apparent sense of how to convey the material, no apparent viewpoint beyond that he was paid to administer tests and to grade them.
In addition to being a bad teacher, he was a jerk. He took great delight in the fact that he failed 30-50% of his class every year (as he gleefully announced first day of class, "I've seen most of you before, and I'll see most of you again"). He assigned problem sets, but just assigned a grade, so you couldn't figure out what you had done wrong. He was famous for turning his office light off during supposed office hours, not answering your knock, and then skulking out when he thought you had left. He once took points off an exam because I switched from pen to pencil to do a side-derivation of an integral.
And now we come to my point. There was no point in doing anything about it. The powers that be knew he was a terrible teacher. How could they not? Other teachers would openly joke about it, or listen with knowing smiles if you told one on "Rusty". For whatever reason-- probably tenure-- he was allowed to stay. Or maybe they liked the fact that somebody was doing the hard job of winnowing out each incoming freshman class to a more manageable size by junior year.
But since it was widely understood he was a terrible teacher, it didn't really matter. Nobody cared if you flunked his class two or three times before making it through. And there was a great instant camaraderie to be found with fellow-students across all the years, just swapping stories about "Rusty".
And you know, a few years later, after I was able to let go of my anger about it, it at least turned into some good stories. Five years on, it didn't matter to me, anymore. And 30 years on, my only regret is that I didn't learn the material better.
In the big picture, you might think about it this way. You go to college to prepare for your future. An obvious part of that is mastering the class material. But part of it is learning to encounter people who are terrible at what they do, figuring out how to step around them, and figuring out whether you have any power to move them out of the way for other people.
To be more specific, I would start by having an off-the-record conversation with another professor you trust and like (if there aren't any, then either you're in the wrong place, or you're doing it wrong). Try to get a sense whether there's a broad understanding among the faculty that the malefactor is a bad teacher. If there is, but it's accepted, then just give up. But if there's some process under way, you may be given the name of a particular person to whom you should speak-- somebody may be developing a case against him, and ask you for specific information.
Oh yes, and a lot of universities have an ombudsperson, who is there to help students navigate the administration. That person generally should be isolated, organizationally, from the teachers, so that you don't have to worry about confidences being revealed, or personal politics coming into play.
Good luck!