Perhaps it's because I've done the vast majority of my globe-roaming solo. Maybe it's just in my DNA. But it became clear last year when someone (lots of people, in fact) finally alerted me to the fact that reclining one's plane seat is widely considered rude. Until then, I'd been doing it all my life, clueless - given I don't at all mind when the passenger in front does it to me - that I'd been causing grievance.
