I suppose there are a few customs, rather than rules, that relate to your choice of position in the above photograph. If this were the situation I discovered, I would use the one on the left or the right so that if someone else happened in, they could attend to business while maintaing some personal space. If I were on the left, for example, another visitor would probably select the right, not the center. I mean ... with a choice, why would you elect to be right beside someone? Harumph. It's not a rule though - just a custom. If you have no choice, well ... then you have no choice, but it's never good form to check out your neighbor's ... um ... package.
What really irritates me are all those men who can't bring themselves to flush that urinal. What is wrong with you?! If you're afraid to touch the lever, get a paper towel to shield your hand, but for crying out loud, flush the damn thing!
There are actually six urinals in this restroom, and I have arrived when none of the six had been flushed. If the truth be told, I flush them all and then wash my hands before attending to my business - followed, of course, by another handwashing.
But really. Is it too much to ask that you FINISH WHAT YOU STARTED?!
There ought to be a rule. Or a law.