This isn't a new thing for me and I'm sure you are all familiar with it too, but as it happened to me yesterday it brought this phenomenon to mind again.
I was going to post a letter, walking along the path, minding my own business. A woman passed me and as she did so said, "Good afternoon."
I didn't reply. Why should I ? It isn't a good afternoon. As usual it's a terrible afternoon and I don't want to exist. Even if I had a great life, why should I reply and what gives anyone the right to go around talking to people they don't know ?
Even when I have been feeling alright in my existence and I may have replied in the distant past, I have always felt it's an intrusion.

What is the intention of these people ? Why do they do it ?
It's a concept I have never understood.
I feel, "I don't know you, so how dare you talk to me and invade my life ?"

What are your thoughts on this sort of thing and how do you deal with it ?