Then there is the opposite of prosopagnosia;
not the incapacity of recognizing familiar faces, but recognizing familiar faces that on second glance aren't. Which made me believe that, unique as we may be, many of us have a number of duplicats walking this earth.

To be touched on the shoulder by someone who says : "Hi Annie", and then: "Oh sorry". Or the other way around: greeting a passer-by enthousiastically who raises astonished eyebrowes.
There is no expression or word for this phenomenen as far as I know.