Another one on the Leave camp. One thing is when someone inadvertently starts to do it (and you may be in a position to give them constructive feedback). Another is when they keep on doing it, and no one on the powers that be realizes. Happened at an otherwise great workplace - at least two other very competent people left, and made it clear on their exit interviews that the person's toxic behaviour (which I just learned to have a term for) was the cause. Since then, the person has been promoted for their "loyalty", no matter how obvious it gets that they get zero things accomplished and cause talent to bleed, so no regrets.