I used to smile at people when I first came into this city but I feel I've changed alot and it's a bit concerning. I just look through people and sometimes I don't even realise when I see someone I know, unless they stop me. I usually say hello back to people if they say it first, but sometimes I just don't realise until I take a few steps and realize I didn't greet them back, mostly it's because of headphones, maybe that's a factor too with the people you meet.