The barista wears her Starbucks uniform and stands behind the counter taking orders and providing drinks. A barista has a limited set of repeated physical movements: taking orders at the cash register, filling cups with coffee behind her, moving around behind the counter.
A customer uses a different set of movements. He stands at the front of the counter until he orders his drink, then he moves over to the side table and adds milk and/or sugar and either leaves the cafe or sits at a table. These are the movements of a customer, not a barista. Rarely if ever do you see one behaving like the other. Everyone in the cafe plays his role and knows his role without needing a script.
If you see a barista acting like a customer, the effect on you is something like "role shock," because the actor isn't playing his expected role and that causes you some amount of surprise.
Whenever we go to a public gathering place, like a cafe, we are tempted into thinking that everyone else we see is what they appear to be based on these expectations. A barista stands behind the counter. A customer sits at a table. When we see what we expect to see, we make assumptions about that person. But you never know who those people around you really are. They could be multi-millionaires. Famous is some field that you know little about. Maybe they just got out of jail after serving a 20-year sentence for murdering someone?
But sometimes assumptions are wrong. For example, real people sometimes work as living mannequins. They sit or stand inside store windows and don't move a muscle. You stand outside the window and think they are just non-living mannequins and you don't realize they are real people pretending to be fake people. Street artists can be living mannequins at times as well, pretending to be statues in public places in large cities. You expect a statue or a mannequin, but you're wrong. It's a real person playing that role and defeating your assumptions.
Stores have mannequins in their windows, but cafes like Starbucks don't use such things. I've never seen a mannequin inside a Starbucks window. Real people in Starbucks are baristas or customers and that's it. You would never see something like a mannequin sitting at a table with the idea that the customers would think it's a real person. You would never see that in Starbucks because why would they? They're more into shaping behavior and so forth with messages on coffee cups. It's the sort of thing an eccentric local cafe owner might do for fun. One could ask, why do those fashion stores employ living mannequins?
Would you expect to see that in your favorite cafe? A person seated at a table, but you notice something peculiar about her. If you could inspect her at close range, you would discover she's just a mannequin. I suppose a group of customers could bring a mannequin into Starbucks and try to persuade the others around them that it is a real person, for their own amusement.
In the future, robots will look very much like humans and will at times be programmed to pretend to be one of us and we won't even suspect the truth.
The regulars in a cafe play their roles. The homeless guy. The computer nerd. The girl typing her emails. The game player. The old people reading the print newspapers. It's as if they are playing a part in a movie with an unstated script. They perform all the expected physical movements and social behaviors you would expect from someone in that role.
But suppose they really are playing a role? Suppose they want you to think they are one kind of person when they are another? Suppose they are spies pretending to be a typical person sitting in a cafe? Suppose they are collecting information on you? What would they be after that you want to remain hidden?