If someone is invading your personal space - say so. Though to be fair, I may be able to put my bag down on the floor but I may not be able to move my butt far enough to suit some people.

I think this is about getting hurt by this lady. If M was getting hurt, she has a right to say she's getting hurt and to ask the person next to her stop hurting her. And she's mentioned that she feels like that was taboo due to the weight of the person. Though I don't think any reasonable person would willingly continue to hurt someone, once told that they are. If they did, THAT would make them rude. And that's the issue, not the weight of the person, though from some of the comments since, it seems as though the weight of others is considered an imposition on some.

In my opinion, that's pretty rude too.