Let's Settle This – Who Gets To Use The Aeroplane Armrests?

A lot of travelers are uncertain of the proper protocol for the middle armrests in rows with three seats. 

Is it rude to recline your seat? What’s the best way to ask a fellow passenger to switch spots? What about taking your shoes off during a flight? 

There are seemingly endless etiquette considerations in the world of commercial air travel. Although some rules and norms are obvious (no, you should not snack on your smelly canned tuna mid-flight), others remain less well understood.