let me just say

I mostly pretend not to see people, outside, when walking around.  It is a selfish thing because it forces all my interactions with mere acquaintances to be ones they initiate, so I know that they actually want to talk to me.

It is an unselfish thing because I know it makes things easier for a few, just like me.  We don't need to acknowledge that we know each other, we know, we know.