I walk to work nearly everyday, and over the course of 1.6 miles each way times over 200 days a year I occasionally come across other walkers/runners etc. It never ceases to amaze me that people when walking/running in pairs do not move into single file to allow those of us going in the other direction room to pass. I would say >50% of the time I end up walking on the grass to avoid contact.
This morning two women were walking dogs (one each). These were rather large dogs. They had plenty of time to see me coming, but they did not move into single file. I was pinned in by a fence and could not take my usual tact. As I passed - the one dog actually lunged at me and nipped at my shorts. In my frustration I actually yelled back at them (as they kept on walking) to "learn to share the sidewalk" among other things.
When Hoot and I were vacationing in Rome, we made fun of the Italians being so intent on their conversations while walking that they never moved for walkers in the other direction. Turns out American are worse, they don't move and have no reason.