Professor mind games drive me crazy.
I had one prof in 3rd and 4th year that just enjoys failing people on midterms. He then allows you to raise your grade by re-doing the midterm and handing it in. The first time, we all freaked out. By the third class we took from him, it wasn't even stressful. It was like "Oh, I got a 45%, but I'll bump it to a 70. No biggie."