I don't mind my airplane seat neighbor using the shared armrest. "why yes, friend! By all means, use the device meant for holding your elbow for it's intended purpose! Goodness knows I'm not gonna use it!"
However, I would have a problem if someone went further than that. If you extend past the armrest, you are invading my space. This little square is all mine, as I paid for it. I don't care if I'm skinny enough that I'm not using all of it, that's my emotional support air.
On that topic, be sure to thank a good seat neighbor! There are a lot assholes on planes, and your neighbor wasn't one of them! Kutos!















