Gym teacher ran a friend of mine to death right in front of me. He had a brain aneurism. That was when I was in fourth grade.
I had a highschool chemistry teacher that failed two whole semesters of students with botched and terrible curriculum management with substitute teachers that had no instructions. The teacher had his wife diagnosed with late stage terminal cancer but was a year away from retirement. The lack of any reasonable safety nets for such a terrible situation wrecked many students lives mine included. How the whole situation was handled was so bad I hated anything academic related.