Right now I have an excellent one, but I can think of 3 real jerks.
First one was a physics prof. Average score on his tests was usually around 24 points OUT OF 100! High was typically about 34 or 36. This guy would start just about every lecture with "as any IDIOT knows..." then proceed to explain a very complex Physics equation that most of us had never heard of. "Idiot" and "stupid" were huge parts of his vocabulary and not a lecture went by without him using at least one of those words at least once and always directed at either a student or group of students or the class as a whole. The guy totally *ruined* electromagnetics for me, and it took me 4 years to recover my self esteem in physics that he destroyed in that class. Luckily, I've had a couple of really good physics profs since who were able to undo the worst of the damage, but to this day I still cringe when I encounter anything physics dealing with electricity and magnetism -- and this is coming from someone who LOVED (with capitals all the way through) physics before this class.
Then, my senior year, I had another jerk. This time to my advantage, though. I was taking a GPS (Global Positioning System) class as a geophysics student in an aerospace engineering class (along with 3 other geophys students). This guy was so biased against non-aerospace engineers that he was bound and determined that anyone NOT in aerospace engineering could absolutely NOT pass his class without him grading easier, so he automatically gave non-AE students a different and easier curve.

Had it been any semester but my last, I would have proven him wrong. But I was hit with a major case of senioritis, so I said "you're practically guaranteeing that I can NOT fail this class even if I try? Why should I bother?" So I didn't bother. Didn't even attend more than 1/3 the classes, and I still got an A.
Then, two semesters ago (and the semester that made me decide to leave the pseudo-Master's program I was previously in and change to the program I'm now in and LOVE!!) I had the second biggest jerk, following right on the heels of the physics prof. This one was Java, and I swear this jerk couldn't write a Java program to save his life.

He was a pathetic professor, wasn't any good as a teacher, ended up throwing out half the questions on each test as being ambiguous or poor questions, and pulled this horrible stunt during the final that sent me to the dean of students in complaint for the first time in my life. Just thinking about this jerk still makes my blood boil. Telling students who are working that they can't return to work until the full 3 hours of the final is up even when the final only takes 30 minutes, and NOT GIVING ANY WARNING OF THIS was the first straw during the final. If he'd said at the beginning of the semester that you had to stay at your desk until the final period was up even if you finished, that would have been fine -- we could have all arranged with our employers to accomodate that time. But to give NO NOTICE of this and then try to tell those of us who were expected back at work two hours later that he was going to hold us in the classroom and we'd automatically flunk if we tried to leave AS he was handing out the final was pathetic and totally unacceptable. THen to say no one can go to the bathroom for 3 hours, and if you can't go that long without going to the bathroom then you will be sent to the nurse's office where you'll be given a BEDPAN and a HARDER TEST was pure discrimination against those with bladder problems.

I don't know if the dean ever did anything about this prof, and now that I'm not there any more, I don't care.
But, out of all the profs I've ever had, those are the only three I'd lable as jerks. And I have twice that many that I'd lable as FANTASTIC, three I'd consider true Mentors in the best sense of the word (one of those is the prof I currently have), and the rest are either great or average. As a whole, I've had good experiences with profs.
