Comment by softwaredoug

I wrote a list of dangerous things to look out for in toxic colleagues, trying to be objective, so as not to think anyone I'm annoyed by is "toxic"

Inability to apologize / repair was near the top of the list. Everyone makes a lot of interpersonal mistakes. Most people can apologize.

Another big one was "norms for thee, but not for me". As in the rules we create as a team don't apply to me. But apply to everyone else. The toxic person gets to use them as a cudgel, but they don't seem to be bound by them.

Another one is being very thin-skinned. Easily jumping into a kind of victim mentality (surprisingly common even in leaders) where they are the ones being put upon. Being a victim, they are justified in doing whatever it takes to correct the situation

Related to that last one, many of these folks feel like they're taking on more than their share and have to carry the team. They may have a narrative they are the brilliant person on the team that has to fix everyone else's screwups. Or the team can't live without their unique skills. Therefore they're "special" and get to act outside the rules / norms. And other leaders can feed into this when they think the special person is indispensable, turning a blind eye to their bad behavior.