I am almost always on the Aisle and the number of totally oblivious individuals that board and "turn"...is astounding....often not even realizing they have whacked someone.
I will shout out to them along with keeping my hand and "guard Up" as they traverse the aisle...not exactly a relaxing scenario.
The perk of being able to board early and secure your overhead space is greatly diminished by these buffoons.
Sadly they are everywhere these days....elevators, grocery aisles, stairwells.....
I have on occasion commented to a few of those who do right (a rare few) who properly remove the backpack outside the entrance to the plane and carry it low...directly in front of them... considerate of others and aware of their environment.
It is all a matter of thinking beyond yourself and what only pertains to only you.....couple that with an electronic distraction....Give it a head's up.
Oblivion...not an admirable quality.