I've had this happen to me a few times. Once, in doggie, I pissed all over my bed and another time the man fucking me sprayed my face with my own piss. So awesome.
It's nice when you can find a top. That's not afraid to do this for you. I was riding a man one time and it just let loose all over the place. He rubbed my face and my own piss on his belly and I slurped it up. It was the only time I got erect. I usually stay limp when there's a man inside of me.