Missing Stair

"Missing stair" is a metaphor often used in the kink/BDSM world to indicate a person that has (sometimes unconfirmed) stories around them of predatory or abusive behavior. Often, no actions can be taken against them due to grey areas or other causes. This results in a situation where if you're in the know, you'll be able to cautiously step around them, but newbies won’t know to watch out and may become involved in a bad situation.

Often a missing stair is known within a community and people may inform people around them about what they know. This may also transfer between communities when it becomes known a person is moving to other communities. However no action is taken against them for a myriad of reasons.

Origins of the term

The term refers to people living in a house may know in the dark basement that a stair is missing, and they won't trip. Whereas a new visitor to that house is likely to trip on that missing stair.