I'd say for men it has to be the unwritten rule of who uses what urinal in the toilets.
A very quick explanation of urinal etiquette: If somebody is using a urinal on the left (person 1), you must use the urinal that is the furthest away on the right (person 2). The next person should then use the middle urinal (person 3).
If a fourth person comes in and wants to go to the 2nd urinal in between urinals 1 and 3 (occupied by person 1 and 3) then they must resort to using cubicle, without making it obvious they they never intended to use the cubicle. They must make it quite clear to all men in the toilet, that they wished to use the cubicle from the moment they stepped in the toilet. However, if the cubicle is not free then they must wait for either person 1,2 or 3 to shake out and step down and take their place. NOT another one such as urinal 2 or 4, as this will be directly next to person 1, 2 or 3. If they were to do this, then when person 5 walks in, they will not be able to use urinal 3 or 4, since they will be peeing directly next to the person in urinals 2 or 5.
Or, they must wait for the cubicle to become free.
You must also look at the wall directly in front of you, as if you're examining it for cracks. You must only look down when you've stopped urinating and have progressed onto the shake. Too much shaking is forbidden, that's a sign of masturbation.
Although peeking is not strictly forbidden, it is definitely forbidden to get caught peeking. Us males have to 'size up' the competition so peeking will always happen. Even if you think that you did not get peeking at somebody who is very well endowed, he WILL know that you've peeked. When you walk past, you'll give each other 'the nod'. This is his way of saying 'look mate, I know you peeked - you know what I'm packing, so let's mention no more on this topic'.
Alternatively, you can walk out and say to your mates 'oh my god I was standing at the urinals and this dude just came in and peed right next to me, he had the smallest knob too, he was pretty much peeing in my urinal, I didn't peek but he was just so close. Look, that's him there' (then point to the guy) This puts you at a higher level in status of being an Alpha Male, but you do risk being confronted about making these claims.