It is rude to sit in another persons seat.
Brenda is on a plane.
Brenda wants to have a window seat.
Brenda asks someone if in a window seat if they would be willing to trade.
Brenda sits down in a window seat even though it is not her assigned seat.
The person agrees and the flight takes off as scheduled.
The flight is held up as Brenda and the person who was assigned the seat get into an argument.