when I'm sitting next to a large person who has spread out over both seats, especially if they have raised the arm rest, I know I'm in for a difficult flight. However a few times on US owned airlines where there is a charge to have a drinkie, a very nice larger person has compensated me for my trouble by buying me a G & T.

Let's call it a negotiated peace settlement!

If the situation is really unpleasant I do ask for help from a flight attendant, but sometimes there is nothing that can be done. Just because I'm not covering all my purchased space, doesn't mean it's up for grabs.