I catch myself doing it sometimes.
When I'm not feeling like I'm at the top of my game, I will tend to not look people in the eye quite so much. I don't think it's painfully obvious, and it's in situations like at a checkout, where it just seems easier to concentrate on getting my card swiped and PIN punched and getting my stuff to make way for the next person in line.
Yesterday, Mr W and I went downtown to get ice cream (a standard summer evening endeavor around here) and we were in line at the ice cream shop. I was doing it, looking at the menu board, looking into my wallet, and finally, when it was time to hand my card over, I looked at the scoop jockey and she was smiling and friendly and I thought, "Geez, is it too much to function as a kind person here?" No, it's not. I have been getting a little self-absorbed with the stuff going on and it is often that I have to remind myself to get back to the business of living this life.
So now that it's at the front of my mind again, I'm going to look folks in the eye, and smile when our paths cross. It's OK that my inclination at the moment is to kind of turn inward, but this is a really good exercise to stay focused on the present.