A yet-unnamed rule
You're walking down the sidewalk. 100 yards away another person is too, and they are approaching you. Between the two of you, not quite in the middle, there is a telephone pole and a newspaper vending machine partially blocking the sidewalk such that two people couldn't pass through without rubbing against each other, a clear breach of sidewalking ettiquette.
This rule states that, regardless of the pace or varying distance of the obstacle, the two approaching people will arrive at it at the same time, so that one must stop, or step out into the street.
I'm accepting suggestions for a name.