…when a person will take on the traits, mannerisms, and Idiosyncrasies of the person he’s interacting with just to please them or to make them more comfortable by pretending hes one of them?
I think most people do it, albeit subtly. Watch the eyes of a crowd when they are listening to a vivacious person relate a story in a very animated way. Their eyes open wide with his and their jaws drop when his does. Also, friends seem to pick up each other’s laugh.
cornelia otis skinner wrote about the difficulties of having this habit (compulsion?) in one of her autobiographical books, either “the ape in me” (1959) or “that’s me all over” (1948) but i don’t remember if she used any particular term to describe it.