Not that I would consider urinating on my kit but...
Random piece of information: Unlike other bodily fluids or solids urine is sterile unless you have some medical condition.

As far as I remember from a first aid course i took a long time ago
If you get stung by some sea creature heat decomposes the poison.
And if it is a land creature then ammonia can decompose the poison.

So urinating on your hand or leg or whereever you are stung might be a good option to get rid of the poison. But should be done in private preferrably...