I have very little sympathy for POS infringing on other passengers' seat space having been suject to this situation more than once in the past.

Even with minimal expectations of economy air travel in the US I would think few Pax would be willing to spent, for example, four hours literally enveloped by a POS "flowing" onto a Pax.

In one case I had to deal with a sweaty and smelly POS (a side effect of bad circulation and various skin issues) who had raised her armrest before I got to my seat as the last Pax boarding the flight; it would have been impossible to lower the armrest after her sitting down.

I am quite tall yet of normal weight and so to speak had nowhere to go. To add insult to injury: The POS began passing gas midway through the flight. Before you ask: The fliight was full and the last flight out of Dallas on a Friday evening I managed to get on on short notice.

I still remember this flight seven years later. America has not become slimmer - quite the opposite - but luckily I find myself mostly upfront these days.