In both a three-seat configuration with six human arms and only four armrests, or a two-seat set-up with four arms and three armrests, the result is inevitable – someone's appendage will be left dangling.
Should the passenger in the middle win rights to both armrests as consolation for having such a dreadful, perk-free seat – leaving the aisle and window passengers with just one each? Do you even care about the welfare of the person in the middle seat? What's the polite way to stake your claim, or tackle an aggressive armrest hogger?
The case for the middle seat passenger
Etiquette consultant Jo Bryant argues: "As a general rule, the person in the aisle seat has the option of stretching out into the gangway and, as they have an undisputed armrest on the aisle-side of their seat, they should settle for using just that.
"The person in the window seat has the benefit of something to lean against, as well as, again, their own armrest. This leaves the person stuck in the middle, who has no chance to lean or spread, and should thus at least get the opportunity to choose which armrest they want, if not both."
Sounds reasonable enough. But if you opt for just one, which do you choose?
Body language expert Judi James points out: "If the middle-seater only takes one, the person's they take will feel persecuted, and the other passenger smug."
James' conclusion is a surprising one, and plays into the idealistic "greatest happiness principle".
"The mathematical resolution is for the one in the middle to use neither armrest, which will at least leave two other passengers happy," she says.
Every man for himself?
In 2017, footage went viral of a middle-seat passenger who filmed himself aggressively jerking his sleeping neighbour's arm off the armrest and claiming it for himself – much to the horror of said startled neighbour. The Twittersphere went into a flurry, with the bold move dividing opinion. The following year, new footage emerged of two passengers, who both claimed to be lawyers, engaged in a bitter brawl over an armrest on a Monarch flight from the UK to Malaga. Both had to be moved to opposite ends of the plane, such was the magnitude of the fray.
"All animals fight over space and in the crowded social set-up of the airline cabin, every inch counts," James comments. "Space equals status. And the armrest battle is all about pecking-order. Animals that are strong and dominant display a greater 'armpit gap' in social situations than submissive, low-ranking animals, who will self-diminish with their arms clenched to their ribs.
"The passenger, therefore, who snares both armrests and gets to sit in the 'throne' position is the one with the dominant stance – both armpits open and both elbows splayed. Trouble only begins – as with the case of the aforementioned lawyers – when both neighbours are of the same nature."
How to stake your claim
You could just politely ask your neighbour if they wouldn't mind you using the 'shared' armrest between you, and hope they're the submissive sort. "They will care," James remarks. "But they might be too polite to argue."
For travel expert and blogger Gilbert Ott, who takes at least 100 flights a year, it's all about claiming territory as soon as you take your seat, in a non-verbal gesture of superiority.
"Step one, establish dominance by displaying 'don't you even try' attitude," he says. "Step two, claim armrest without mercy. Step three, relinquish armrest under no circumstances. If a bathroom break is necessary, you've failed."
Is there a compromise?
Yes, if you fork out $50 and procure the Soarigami, a portable armrest extender that doubles the usable space by effectively turning one armrest into two.
But are we all making much ado about nothing? Acclaimed etiquette coach William Hansen thinks so.
"The middle passenger should not get both armrests," he states. "This is a common misconception. They are not armrests. They are elbow rests and two elbows can easily fit on one, with your hands then resting in your lap.
"Who sits with arms locked on either side in manner of Lincoln's Washington DC statue anyway?"
At least some of us, apparently.
The Telegraph, London