You think you’re not doing that now? Well, except for the shit part. OK, OK, I’ll let it go.
Yes, it’s sterile and fresh urine is used as a disinfectant if nothing else is available. During this past season of Survivor, one contestant was (IIRC) stung by a jellyfish and another urinated on the wound (not shown on TV, of course). It would probably take quite a while for fresh urine to become non-sterile.
[nitpick]He put his hand down on a sea urchen. He is also a nurse, so he jumped right out and asked someone to pee on his hand.[/nitpick] Funny thing about that is that the urine stops the stinging in mere seconds, but, as you know, once you start peeing, it’s sometimes hard to stop and the guy just sat there getting peed on for another 10 seconds or so. Heh.
Urine does work on jelly fish stings, though (and is supposedly good on athletes foot, too.)