common courtesy

Early this morning on the tram as I watched a fellow passenger take one last huge drag off of his cigarette and then exhale a cloud of smoke inside as the doors sealed shut, I began to wonder: where do we learn common courtesy? To me, what he did was incredibly obnoxious and inconsiderate. To him, apparently it was perfectly acceptable (which leads to another question: is he just oblivious or is he an asshole? Because in my mind, those are the only two possible explanations). Why is that? When do humans learn proper behavior? How are they taught? I don't recall my mother specifically teaching me about common courtesy or respect for others, maybe I just learned by observation? Or did we learn it at school? Or maybe it's innate… or not, for some people? I do recall public service announcements on TV when I was a kid but, despite their catchy tunes, I honestly don't know if those had any impact on me or my behavior.
I'm genuinely curious about how, as a society, we can help people be more aware and more considerate of others. Since I've been back in Rome I often find myself observing people's actions- from illegally dumping piles of trash bags by a tree, to leaving a dog shit obstacle course, to parking wherever the hell they want- while wondering: What makes you think that's okay to do?