It's hard to say whether or not this particular passenger was in the wrong in this situation. The story is bizarre. Take a look at this odd Reddit story.
I was taking a long flight (8 hours) last week. I boarded the plane and took my seat, soon a woman came and took her seat next to me. Now I am all for body positivity (everyone is beautiful) and I do not mean any offense when I say this woman was extremely large.
I’m quite a small person and I was a little nervous about sitting next to her but of course I didn’t want to assume anything negative and hoped for the best. As soon as she sat down I realized this arrangement wasn’t going to work.
The seat clearly couldn’t accommodate her size and she was spilling out on both the aisle side and onto my seat. When the flight attendant asked us to put down our arm rests I literally couldn’t do it.