I had almost the exact same thing happen to me, except it was my item that got pissed on.
A long time ago I knew this punk rock girl named Jenny. She was a mess. At her place, in her own room, the foot of her bed faced straight towards her bathroom. In my room, at my house, the foot of my bed faced towards an ancient gas powered space heater that was permanently fixed to the wall. So she was passed out in my bed one night, got up, walked to the heater, dropped her pants, pissed all over it, and stumbled back to bed. I have to assume that she was so out of it she thought she was in her own house, in which case she would have made it to her own bathroom. But at my house she pissed on a heater. It wasn't on though. We don't need any heaters down here. I made her clean it up the next morning or she was gonna have to walk home. We never fucked again.