A situation when one takes an incomplete shit, leaving a protruding “turtle head” behind. The shitter then must pet the lodged turtle head approximately 70 times with toilet paper or moist wipes, shitter’s choice of course.

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.