Recently, I wrote a short play-ette in my A. Playwright's Rambling blog, focusing on the encounter of two women shopping for lipstick. Although it was exaggerated for drama and content, it was based on a real-life encounter as are many of my "Scenes from Real Life" Life experiences lend themselves as fodder for drama.
For whatever reason, shopping carts or maybe it extends to anything with wheels, seem to bring out the inner beast in some people. Perhaps it's a skewed feeling of power in that they control a vehicle be it a means to hold food items, which could in theory give them muscle over other shoppers. This is particularly noticeable when lining up at the cash to pay. During a big sale at a supermarket, I watched two females (but it just as easily could have been males) actually sling verbal accusations at each other focusing on who was went before while waiting to pay. I mean, really.
Related to this is the quest for parking place and the need to be close to a mall entrance. Shoppers for whatever reason - laziness springs to mind - will drive around and around in tight groups, one car behind the other, ready to spring into action lest a car be spotted pulling out of a space near the door. As a shopper I've been followed by a lineup of ve-hi-cles while walking to retrieve my car. Usually, it's located two rows over from where I'm searching and upon arrival at my destination, the cars are already waiting for my departure. What's the difference if you have to walk a few feet more is my philosophy.
Thinking further perhaps it goes back to our basic survival instinct in that we feel the necessity to exend our superiority and strength in social situations. A shopping cart gives the customer control be it in a limited fashion, over her/his immediate environment. Then again, a parking spot is a parking spot is...unless of course it's 20 below zero in a snow storm. Then it's every man or woman for themselves.