What is the association.
Is it as simple as convenience or is it evolution.
Is it possible human used to spit on their genitalia to begin the urination process and this act is merely a shadow of this archaic function. Puppies seem to require a little lick to get the flow going. Maybe people began the same.
Or is it some sort of strange territory marking. Maybe because it would seem silly to piss on the pissing tree to mark the pissing tree as yours you spit on it?
Or could it just be that a guy sees the last mans spit and thinks "I would like to spit as well. No place like here!" I don't buy that. That would imply that a simple cleaning could cause the spitting to stop. But as soon as the urinal is used. Spit.
I also love the fact that if there is a piece of gum incorporated it is often deposited here. So poor shithead (pisshand) needs to pick that out. Is that why people do it? They know some "lesser" being will pick it out so somehow they obtain power.
I don't know. I spit too.