OK, they may not be rules, but they are common courtesy. I have seen all of these in the space of one thirty minute period this past week. Maybe I am just a holdover from a past era, or maybe I am a grumpy misanthrope but these are some of the reasons I hate going to shopping centres in general and the supermarket in general.
First, traffic flow. I know that you may not be on a public road, but please follow the markings and rules in the shopping centre car park. I hate it when I follow the left-turn only signs and other markings (i.e. following the rules) and do a lap of the nearly-full car park only to beaten to the empty space by someone who ignored the rules and turned right against the flow to grab that spot. People like that should have to do a drive-through penalty. Or have their licence cancelled.
Next, once you find a free space, you discover that someone has left a shopping trolley in the empty space. Of course, I appreciate that your time is so important that you can't spare sixty seconds to take the trolley back to the space provided for it, and consequently you must inconvenience both the next person along to that space and the poor minimum-wage sucker who has to lug these things back to the entry to the supermarket. Show a bit of human decency. Inconsiderate so-and-so.
Finally, I'm unloading my trolley at the checkout. Along comes a customer who decides that my checkout line is actually the entrance to the supermarket, rather than the conveniently placed and marked entrance. Can't you even read?
Now you may think that all of these infractions of the supermarket social conventions are harmless; that nobody is hurt. I don't care. We live in a society, where for everybody's benefit we follow rules and conventions. These little things may not make the world a better place or make life-and-death differences, but they do make a necessary task for everyone a little more pleasant.
Don't get me started on people who cross the road ten metres away from a perfectly serviceable pedestrian crossing or set of lights...