Piss goes with everything! It puts the D in BDSM (and also the S if the dude recently ate asparagus). It washes down or washes off cum. It can be enjoyed solo or with your plus one or plus 20. And it cleans tile grout.
Most of all, it's fucking intimate. Take a private thing and literally spray it on someone else or spray it on yourself while someone else watches. Instant intimacy. Even if you do it in an alley or the mall parking lot. Hey that guy hawking cell phones in the mall kiosk was cute. And so much cuter soaked with urine. Thankfully his uniform was polyester.
As fetishes go, it's quite photogenic. A part of a guy (maybe even from some of that wine you two toasted your three-week anniversary to) that he's sharing with you and you with him. Flash forward to a wedding cake with two modeling chocolate figurines of one groom peeing on the other. And remember, if a bakery refuses to make that for you, take them to court. Seriously.
Piss play can be pure play or romantic or prankish or dominant or masturbatory or cathartic or pervy or bonding or messy or precise or secret or public or some combination of all of these.
And judging by the vintage and creative watersports pic above, it's been around a long time and is not going anywhere. Now if you'll excuse me, I have to go pee. Into the toilet. With nobody watching. It's okay, the toilet bowl is totally into it.
P.S. In case this encourages new piss players, I can't help but suggest you talk with your doctor before engaging in piss play (healthy piss is healthy but piss isn't always healthy, get it?). Then ask your doctor to piss on you. You know he wants to. He's always asking for urine samples, remember?