When something is so disgusting the use of that word is not enough. The Pu is short for puke or Pus. When you’re wearing shoes and you step in dog poo it’s disgusting but when you’re barefooted and step in dog poo it’s Pusgusting.

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.