You'd think finding your seat on an airplane would be one of the easiest parts of the flight. Airlines are pretty specific about that. Unlike concerts or some movie theaters where you can sit in one general area, when you fly, you choose your own seat. For those who get plane-sick, there are window seats; for those who want to stretch their legs out and move around, there are aisle seats . No one wants the middle seats, naturally. You can't just waltz onto an aircraft and sit where ever you wan…