Everyone knows he is a missing stair in our office.
missing stair
idiomA member of a community who is widely but privately known within that community for abusiveness or other harmful behavior that has not been addressed.
Origin
first recorded 21st c.Coined by blogger Cliff Pervocracy (a pseudonym) in 2012. In analogy to a stairway missing a step, with guests expected to overcome or bypass the obstacle rather than it being fixed.
We all avoid the manager because he is a missing stair, but nobody ever reports his behavior to human resources.
The community tolerated him as a missing stair for years, silently warning newcomers about his conduct rather than confronting the underlying problem.