someone who claims to be your friend, but is never actually there for you. like a shadowbox, this person (or people) are more like a hollow shell and no substance than a real person.
Person 1: man, i just had a huge fight with Sammy.
Person 2: why?
Person 1: she claims my personality has changed, but how would she know? she's never around anymore.
Person 2: what a shadowbox friend.