Residual urine that is present on an individual after using the bathroom. Because of its sometimes sticky nature, it is attributed to being the juice of a watermelon that was supposedly recently consumed by the individual.

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.