The remainder of goop left over from a massive shit that plopped into the toilet, causing the poo, pee, vomit, bacteria, menstrual blood, and whatever else is in your toilet at the time to spew up into your anus, leaving you with a dripping mixture of FUN.

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.