If I'm walking briskly along, obviously in a hurry to get somewhere, and you wander across in front of me because you're going in approximately the same direction...then that's fine. I am a mature, rational human being, and I can live with another person heading the same way as I am.
But if you wander in front of me and then slow down and/or STOP because you've just realised that you were dropped on your fucking head as a child and don't have any fucking clue where you're going, blocking my path, I am assigning myself the RIGHT to shoulder-barge you to the floor and then jump up and down on your gonads.
Do not fuck with a commuter in a hurry before they've had their morning coffee. Get in my way and you lose your fucking face.