Missing stair is an analogy for a person within a social group who many people know is untrustworthy or otherwise has to be "managed", but who they work around by trying to quietly warn others rather than deal with openly.

A term coined by blogger Cliff Pervocracy.
Yeah, everyone knows about that person isn't safe to be around, they're a real missing stair.
by ceolyn September 23, 2019
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