A typical place would be a petrol/gas station where inside its all warmly illuminated and bright and then you go to leave and you pull open the door someone else is coming through that you haven't seen because you cant see out through the glass because all you see is your own reflection and on top of that its not and automatic door so bang its an ugly confrontation. Many times i have passed people at doors, held the door open for them and vise verse and not realised its someone i know because I'm looking at the ground.
Alex(uk)