I have had one of these (approx 22 stone) pax come along next to me who just lifted the armrest so he could half spill over into my seat. No please, no excuse me, just did it.
When I said "Excuse me, I will keep MY armrest down, thank you", he waddled off to the cabin crew and was found somewhere else, presumably next to someone more timid.
From our CPL friends, what are the actual regs about armrests down for takeoff/landing, as patrolled for by the crew. Is it an official requirement ? An airline procedure ?
BTW I did hear of a gross pax who was made to book 2 seats and was then allocated 10C and 10D, on opposite sides of the aisle !