Yeah, this seems like a pretty obvious issue. I mean, there are two ways to be the best: by making yourself better or by making everyone else worse. What if the other employees, realizing that their company clearly doesn’t give a shit about their well-being, just don’t really feel they owe their company any special effort.
Or, here’s another one. What if that toxic worker is actually just good at taking credit for things? Maybe no one told their manager because they figured that the manager was exactly the kind of incompetent idiot who fell for that toxic person’s nonsense?
And, let’s face it, a good part of the time it is your manager who is the toxic asshole because their “accomplishments” got them promoted.
Human beings! To me, this is the very height of being “toxic” but in most workplaces this isn’t only normal, it’s the way things ought to be. People tell you with a straight face to work on your “personal brand.”