What are seemingly rational people who have loud public cell phone conversations thinking? Do they think: no one can hear me because I'm speaking into a phone. Do they think: people can hear me but because it doesn't concern them they won't listen. Or do they think: If people can hear and bothers them that's too bad, I’m me, I'm important and I need to have this conversation here now.
Of course its most likely that they aren't thinking at all. This is the essence of rudeness to not consider how your actions might effect others. I believe the word is thoughtless, without thought.
Earlier today I had the misfortune to overhear a couple arguing. It was clearly not an issue that needed to be settled then, they could have waited until they were in a less public place. But they were rude. And by the way, the man was a total jerk. He was trying to make his partner feel like a complete idiot.
If you're going to argue at all do it to get your point across and in the bargain pay attention to other person's position. Maybe you'll both learn something, perhaps they'll be a little give and take. Don't just argue to win and certainly don't try to make the other person feel bad.
Anyway, public cell phone calls, public arguments and people who just plain talk too loud are the main reason I usually leave the house with my ipod. Most of what is tuned out is stuff I don't want to hear anyway and I get to listen to Sinatra in the bargain.