That’s interesting! As each person queues in line, they can claim that they are “ready” with items, “ready” to wait, and “ready” to pay. Since she is not “ready” (she can’t pay for what she doesn’t have) then she should go to the back of the line immediately as each person queues up who is “ready”. This is how queues currently work.
Waiting in line is based upon the Scarcity Principle and the Social Proof Principle. If the end result is a scarce commodity, we agree to wait. If others wait, then society has decided that the end result is of value, so we also agree to wait. Cutting and Camping are allowed depending upon the degree of scarcity and value perceived.
Black Friday-type sales, iPhone releases, Beany-Babies at Christmas, are all “scarce” items. Camping is expected; buying large quantities is restricted so camping doesn’t restrict others; Camping and letting latecomers in, along with Cutting, is a death sentence.
Amusement parks and movie premieres are “scarce”-right-now items. Sure, you can wait longer and still get it, but the waiting until later is not what you are paying for. Saving one spot for a bathroom break, car parking, or other logistical necessity might be okay, but the more unique the experience, the less allowed that becomes. Camping and letting latecomers in, along with Cutting, is also a death sentence.
In a grocery store, the “scarce” item is not time per se, but the length of the line. And the length is not the people, it’s the number of items to buy. We don’t choose our line saying “Oh, that’s got 4 people but this one’s got 3”. We use the volume-of-cart method. In a store with one or two long lines, the short line is more scarce. In a Walmart with 30 lines (but only 10 of which are open), the short line is harder to calculate and so you just choose and grumble. Similarly, highways with 5 lanes, traffic, and cars jockeying for place is annoying, but more tolerated, than the guy who passes in the turn-only lane only to cut back in where the off-ramp veers off.
Another element is that waiting in line at a grocery store is a required activity. We have to eat and drink, we get these items at stores, so waiting to pay is a required activity. Waiting longer makes that negative experience more negative. Waiting in line for a park ride or a movie premiere is not required, it’s a luxury choice, and waiting more can increase the excitement and perceived value.
Having finished shopping, moving to checkout, and the spouse scoots ahead to get a spot, waving the slower spouse in line is understandable. People see this is making the line long. Camping out for your shopping spouse is deceiving/robbing people of the scarce item - the length of the line. I with my cart of goods am “buying” my place in line and others who camp or cut are devaluing my investment.
It’s a dick move 'cause you’re stealing my time and I didn’t volunteer to give it away, but I’ll give up my place for someone with a couple of items if I want to “buy” some good karma.