It is a name for someone who has such a strongvibe off them that there is a physical change or difference, like the air shifting when someone walks into a room.
Person 1: you know how Derek is a daddy-in-the-mist?
when you're holding up your phone and making faces at it, as though you are taking a selfie, but you're really taking a picture of the person across from you or the wall or anything else that seems interesting but you don't want to be caught dead taking a picture of.
This action is often made more convincing by wiggling the eyebrows or opening the mouth, to pretend you're trying to get a Snapchat filter to work.