Some of these comments sound pretty demanding. Do not do this or that, do this!

You shouldn't stand in the middle of the sidewalk lest you inconvenience someone by the 1 second it takes to walk around you. You shouldn't stop and look at your surroundings because it's mind boggling that you're visiting the US and actually want to see stuff. You probably shouldn't stop in the stairwell, not even to tie your shoe to prevent a fall which could potentially break your neck because it could inconvenience a couple people who will now probably be late to wherever they were going because they lost two seconds to walk around you. You should probably too 10 to 15% if you feel like it but keep in mind that they won't arrest you if you don't leave a tip, you'll just have an aggravated waiter or waitress who you'll never see again.