Not a girl, but the naughtiest place I've pissed is on my living room carpet. Context, I live with family, but one long weekend, I was home alone, my family being gone from Thursday Morning to Monday night. So, once they were gone, I spent entire time I had to myself naked. And, whenever I had to piss, I just went wherever I was, usually on the carpet in front of me. But the most fun I had was being able to just walk in the door, whip out my dick, and piss on the floor.