The story
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.
Etymology from Wiktionary, CC BY-SA 4.0.
missing stair
Today it means: A member of a community who is widely but privately known within that community for abusiveness or other harmful behavior that has not been addressed. Full definition →