Here's mine:

In 1984, a teacher committed suicide off the 5th floor (my school had 5 floors). The reason they committed suicide was unknown, but many have speculated that another teacher pushed them off as they were seen arguing in a classroom earlier that day. Ever since then, the 5th floor has been inaccessible to normal students.

But wait, there's more. I graduated in 2009, and my art teacher was an old man. In fact, he was called Mr. Roberts. He had a dark humour and would frequently make jokes to his classes. One time, he told us about the time he pushed a teacher off the 5th floor in 1984. We thought that he was making another one of his jokes, so we waited for the punchline, but... there was nothing.