A person, Who after a one night stand, In an act of dominance, While their partner in the act lies asleep beside them, decides to produce a steaming shit on the sheets without waking them, And proceeds to flee the scene, thus making them a Shit Sheet Bandit.

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.