Perhaps it's some of both. I see people every time I travel who just flat out don't get it. (I don't know why it becomes so apparent specifically when I travel...perhaps because airports are packed with people and you really notice these behaviors.)

For example, there is always someone on the escalator, standing on the left, totally unaware that anybody else is trying to get by. Or somebody wandering slowly down the concourse, without purpose, while humanity tries to flow around them. Is this person just a Grade A Jacka** telling the whole world to stick it? Or are they just clueless...?

I think in many cases, it's cluelessness. Maybe the person isn't completely stupid in the rest of their life - or maybe they are - but they lack situational awareness.

Cell phones exacerbate the problem.