Permacrud is formed over a period of years, appearing as vehicle "matures" into a hooptie. It takes years of neglect, regular intervals of pressure from passengers' footwear, and exposure to seasonal temperature changes for permacrud to form.
Once formed, permacrud cannot be removed without removing the carpeting and/or floorboards.
Me: "I did! Do you see any any beer cans or McDonald's bags anywhere?"
My old lady: "EWWW it's gross!"
Me: "It's just permacrud. Get in the fucking car and and work the blinker for me would ya?"