My Sophomore year of High School, I had a Algebra teacher that failed the entire class except two people that passed with a "D" (mind you my class was about 22 people). Of course every parent, Grandparent and Great-Grandparent spoke (and threatened) the principle about this teacher. Since she had tenure she was invincible, it didn't help that she was the department head. After failing the class, I took it again in summer school with a teacher so good, that I mad a "C+" and everything that seemed confusing to me prior, was made crystal clear.
My Senior year of High School, I had a Physics teacher that was so absent minded that he would forget what he taught us the day before. Needless to day at first it was fun to take advantage of it (my classmates would agree), but after a while it was annoying. Again,...he was the department head (and tenured), therefore he was also invincible. I passed the class with a "C" because I had to remind him to apply the extra credit to everyone's final test.
My Freshman year of Undergrad, I got stuck with a Biology professor so bad that her reputation literally proceeded her. Everything I heard about her was true. Guess what?...she was also the department head.
Also in my Freshman year of Undergrad, I took Psyc 101 with the department head. Ironically she was a great teacher, but it was impossible to talk to her one on one. It was like she was a Rock star constantly swarmed by adoring fans. But when I took her Psyc 212 class my Sophomore year of Undergrad, I understood why she was a rock star. Her personality and teaching skills are infectious (but she's Hitler when it comes to grading, you mess up and your grade will automatically drop one letter).
What great luck I've had with department heads.