I had a similar experience flying with AA from LAX to LAS last week. The gentleman in the window seat was a person of considerable size and as a result it was rather uncomfortable for both the chap in the middle seat and for me in the aisle. Fortunately I was able to move into the row behind and the occupant of the middle seat moved into my now vacant aisle seat. It was the best course of action in the circumstances, but only available to us as there was a spare seat.

My view on all of this is that people are different shapes and sizes for all sorts of reasons but I would have hoped that people of size have the self-awareness to either book into a premium cabin or else request an additional comfort seat, both for their benefit and for the benefit of those who might otherwise be impacted as a result of their girth.

I have to say, however, that I do take issue with the title of this thread and also what I perceive to be "fat-shaming" by the OP. I think the same points could have been made in a less sensationalised manner. I also fail to see the relevance of the "inevitable American" comment which strikes me as a form of racial stereotyping!