Briefly, "the realization that each random passerby is living a life as vivid and complex as your own." Originally from the Dictionary of Obscure Sorrows, which has a lot more beautiful neologism definitions like this you might enjoy.

A new race aqiured by not wanting to be any other race

When you dress up as a steampunk clown and join a bunch of action figure trading groups on Facebook, then never actually post in any of them other than one snarky comment on someone’s post every once in a while.