new rule

If you're walking on the sidewalk in New York City and taking up more than a normal amount of space—if you're walking with a friend, say, or if you're obese—you must make sure there's room for people to pass you.  There's no such thing as a one-way or single-lane sidewalk in New York City and no normal circumstance in which another pedestrian should have to duck into a doorway or cross the street in order to share it.  And if there are three or more of you, a helpful rule of thumb might just be never to walk side-by-side on a city sidewalk; if you do, you'd better damned well be keeping an eye out and ready to let people by.  My favorite / least favorite reaction is the one you get if you're trying to pass four people (inevitably tourists) taking up the whole sidewalk, so you say, "Excuse me," and they're like, "Whaaaaa???"—like, practically bowled over with the shock and surprise—as if you'd just come up to them and said, like, "Quick!  Hold my scrotum for me!"

"Whaaaat???  Somebody needs to get by??  My gosh, you were right: New York City really is a Hobbesian nightmare!"  (Because your average tourist would use the word "Hobbesian" in a sentence.)

This rule also applies—dear masticating Jesus does it apply—on subway-system staircases.