This is going to rock your world... if you're a woman. Here's the thing: when guys walk into a public bathroom, we draw on gaming theory to determine which urinal we will use. And almost every guy will pick the same urinal, given the same set of circumstances. Even stranger, this jockeying for position requires virtually no conscious thought -- in fact, thinking about it too much can disrupt the process.
Rather than try to prove this with the strength of my prose alone, I am providing a visual aid and scenario role-playing; guys, tell me if I stray from the true (and ladies, you can ask your man about this; he may try to avoid the question, but we can't deny our instincts).
Guy walks into the bathroom. It is unoccupied.
Any urinal is acceptable, as long as no one else is there. And if someone else comes in, there is always room for an empty urinal between the two guys.
Guy walks into the bathroom. Urinal #1 is occupied.
#4 is the first choice, and #3 is acceptable if #4 has not been flushed. Guys will not choose #2.
Guy walks into the bathroom. Urinal #2 is occupied.
#4 is the only acceptable choice.
Guy walks into the bathroom. Urinals #1 and #3 (or #2 and #4) are occupied.
There is no acceptable urinal. Wash your hands for a while and wait for an opening, or use a seat. Or just hold it until you get home.
You're the only one in the bathroom, and you're standing at #1 (as is appropriate). Some guy walks in and, though #4 and #3 are both clean and available, he steps up to #2.
What do you do?
Halt the flow, zip up, wash, and get out; don't look back.