When you are not one of them, dealing with them in public can be extremely frustrating, simply walking along the street at a normal non-zombie pace takes considerably more effort than it did 10 years ago because it's one way navigation problem... it's like that film "Surrogates" where Bruce Willis breaks the mould and goes out into the real world to walk among the surrogate robots, it's basically the same problem (insensitivity to their surroundings), that film was spot on, the only difference is that it's little glass rectangles and mind manipulation instead of robot surrogates.
That's the most obvious example, but it extends to everything that people do in public, simple things like waiting for someone to get on a bus, trying to cross the road, trying to go through a door, and even driving... it's gotten to the point where rather than simply an annoying distraction, smartphones are now the main focus for many of these people and the real world is a distraction. The other day I got a scornful look from a woman in her car as I was forced to beep my horn multiple times to prevent her from rolling into me as she was staring down intensely at her phone at a traffic light, as if the urgency of crashing came second to her fucking facegram feed, it makes me want to slap people around the face to wake them up. I hate hating people but it's impossible to avoid this now.
Then again, I've never been a smart phone user, so perhaps this difference is more noticeable to me than those coming back to the real world.