It's always weird to look at the pop culture symbols we just take for granted and realize how often the origins are somewhere between insulting and utterly horrifying.
It's freaky when actual animals turn into serial killers, stalking prey and evading capture in a way that makes the shark in 'Jaws' look like an incompetent asshole.
Teachers are people, too, and people have this nasty tendency to occasionally lob whatever untruth comes flying at them right back at somebody else like a game of bullshit ping pong.