Who Gets the Armrest on the Plane?
The fact is, those armrests are so narrow they're barely enough for one person. In a row with three seats across, the passenger in the middle seat has it tough enough, so let that person have both and just keep one for yourself.
If it's what they call a 2x2 configuration, there's more at stake. Which of you gets the shared armrest? If your seatmate seems intent on using that space, take a minute to assess your priorities: Do you really need it, or are you fighting on principle?
For short-haul flight, I say let it go. On a longer journey, I find that a couple of well-timed nudges early in the flight usually make your seatmate willing to share. Should you find yourself in a battle of the elbows, again, take a minute to assess whether this is a war worth fighting.
If the answer is yes, the best option is directly saying, "Do you mind if I get some space here?"
Don't check your common sense at the gate. Learn the golden rules of airline etiquette from the experts