Most people, if they have any spacial or self-awareness at all, would move to the other seat, leaving the middle seat empty. But, though it's rare, there are some people who don't seem to subscribe to this type of seat etiquette. These are our travel nemeses.
We've all sat down next to a person, whether its on a plane, or bus, or Uber Pool, who doesn't seem to understand leaving a space between other riders when the opportunity presents itself. You may ask yourself, "Who is this person? Why are they like this?" These are people who live and breathe chaos. After all, who in their right mind wouldn't take some extra space when it's presented to them? Humans are not meant to live like sardines.
Frankly, basic etiquette suggests that people should leave personal space for others when it's available. While we understand that not everyone identifies with the same definition of "personal space," most airplane seats are, frankly, too small not to move over. It not only allows the person next to you to get comfortable, but it also allows you to get comfortable. Win-win. According to etiquette expert Diane Gottsman, a personal bubble of two to four feet is generally best. Obviously, this rule can change on a bus or train, or if you're sitting next to someone you know well.