When you bump into a chair that has a person sitting in it, they feel it. It does not matter which part of your body you do this with. They feel it. When you rest your feet, or knees, or anything else, on a seat that has a person sitting in it, they feel every single little shift that you make. At that point you are taking up more than your allotted space and you are affecting the enjoyment of another human being.
If everyone could spread the word about this, that would be lovely. I’d like to be sure everybody knows.