Irony, as a word, is often misused, but frequently invoked nonetheless. But as a thing left unsaid, it's at least amusing, and sometimes inspiring. It's the sort of thing James Joyce wrote in his notebook, the minutia that made his writing so insightful, specific, and intimate. It's these details that make up the jokes in life, make things seem a touch sitcom-y.
You notice these moments - or don't notice them - because they happen anywhere, everywhere, and all the time. It's someone asking you to justify paying $110 for running shoes, perched on an $8,000 bike. It's amusing, because the joke isn't said, and because it's not really a joke at all. There is a genuine inquiry, a point to be made; but that point sticks its wielder.
A coffee bar might as well have a glass visage in front of it, for all that it approximates a zoo. It gives a blissfully detached view of the human condition, with irony on full, glorious display. Of course, there is not glass visage, and any sense of detachment is pure artifice. The people you watch are aware of you, and probably, they're noticing you as well. And there is interaction too, of course, albeit strained through the filter of customer service, twisted through the fibers of forced smiles and repeated pleasantries.
And so, even when there are words shared, more often than not, some detachment exists. This allows for those sitcom moments to creep in, for the laugh track to sound from imagined speakers, as one (or both) of you stand oblivious to the comedy.
There are skim mochas, and other botched attempts at calorie (and waistline) reduction, ordered by those for whom another ~100 kcals would make nary a difference in either direction. I see that, and I see irony, and comedy.
But the visage is dually transparent.
There is the barista on the other side of the counter - me - necessarily ignorant of the part I'm playing in others' mental comedy. It just wouldn't be as funny if it was on purpose, or even if I knew about it at all. (Hence the lack of specifics.)
In either direction, this is not voyeurism. It is, rather, the sort of thing that makes coffee bars more than the sum of their parts. Coffee is great, and so are people (broadly speaking). But the environment - all of it taken together - makes it the sort of place people like to visit, and like to work at. It's the pithy daggers we needle each other with, insults and slights never spoken, left as private punchlines, that make our shared presence so enjoyable.