The idea of it is hot, and though I enjoy seeing someone pee in their car, the reality of peeing in my own car and the cleaning/extraction involved makes it less appealing. I like a clean, nicely detailed car.
I’ve been tempted a few times in rental cars, but I could never bring myself to do it knowing someone has to detail it before the next customer. I would feel for the next customer. I rented a car on a trip that someone clearly peed in the back seat and on the floor. When the car got hot in the sun, it smelled like a hot piss box, and was just not a pleasant experience.