This is actually how my kink may have started.
Back when I was 6 or 7 I had this friend at the time and we would play in the backyard of her house. This is one of the earliest memories I have, one day she told me: Wanna see something funny? And she pulled down her pants and peed on the grass. Of course she also encouraged me to do it at the time and we did ot many times over the course of a few months. At that time it wasn't anything sexual obviously, but from that first time seeing someone pee right in front of me, piss was never the same for me haha