Now, when I'm walking down the street, I'm seeing where other people are walking. I'm projecting trajectories and plotting my path around them. I'm anticipating their changes in direction due to the obstacles and other people's motion, or due to proximity to shop door-ways, zebra crossings, puddles, etc. What's more, I'm doing this automatically. I'm aware it's happening, but it doesn't take conscious effort.
Other people don't seem to do this. Today, I watched two people walk straight at each other, and have to stop. I've been walking along a mostly-empty wide pavement, and seen someone walk out onto the street from a shop, looking down the street past me, and move into the pavement and stop exactly on the line I'm walking along.
I let people walk into me. Really. I see that they're going to do so, and I just stop and stand still and let them. I'm six foot tall, people, and a good two and a half wide. Why is it you're surprised that I'm suddenly there?
(And it's even worse in supermarkets, when these muppets are armed with a trolley. Given the spacial awareness they display, I'm horrified that the next thing they do is climb into an armoured, self-propelled collision-in-waiting, and tool off down the street at fifty.)
Still, maybe it's Darwin in action. The oil'll get scarce, private transport will be banned, and then they'll all be Hit By Buses, and the problem will go away.
See also: "Dinosaur Cranial Capacity," by Gary Larson.