This one's simple, but super hard to remember: Judge not, lest others bla-bla-bla...
Say, for instance, you see a shopping cart groaning with the weight of a dozen frozen dinners, prepared meats in bulk quantities, giant bottles of soft drinks and voluminous boxes of fluorescent cereals. Here, you think to yourself, is a recipe for obesity, diabetes, heart disease and cancer. Doesn't this shopper know about the carcinogens in prepared foods, about how unsustainable factory farming is, about the evils of soda pop?
Meanwhile, said shopper is casting a jaundiced eye on your cart and mentally tallying up the cost of your choices. Doesn't that person know, they're thinking, that so-called organic products are no more nutritious than conventional ones? Don't they know that all those supposedly healthy foodstuffs are really just packaged status symbols advertising their consumers' socioeconomic privilege? It must be nice to have that much money to throw away, and even nicer to have the time to cook from scratch with fresh produce instead of arriving home exhausted from a full day of dispiriting, low-paid labor to find your kids howling for dinner.
Listen, shopping is a pain and we're all in it together. Better to nod to one another in commiseration than deconstruct the consumer habits of strangers.