Everyone worries about how much legroom they're going to get on a flight, but being able to relax your forearms on the armrest is just as important. Want to make sure your seatmates don't hog the armrests for the entire flight? GQ has some expert advice:
Distract them by dropping a pen near their feet. They'll feel compelled to bend over and pick it up for you, thus removing their arm from the armrest and allowing you to swoop in.
Suggest they turn on their air conditioning. This likewise creates a seemingly helpful situation where you're looking out for their best interests. But when they reach their arm up, go get that armrest!"
Accidentally" touch their elbow. This joint is a sensitive spot, so if you "accidentally" graze it with your fingers while reaching for your seatbelt or buckle, they'll instinctively move their arm away.
Be in boarding group 1, so you can get their early and establish your territory. Then appear glued to your phone while holding your device in the hand of the arm that's draped atop the armrest. The importance of someone's phone is universally acknowledged, so your seatmates are less likely to interrupt you.
Don't acknowledge them or make eye contact. Once that armrest is yours, just keep looking forward. As soon as you 'share' a moment through eye contact, your instinct to be nice toward your seatmate will kick in.