A : Unfortunately,that won't be possible.It's against our policy for passengers to leave their assigned seats on this airline.
B : Well ,that's a crummy policy.I don't get it.Other airlines allow it.Why should passengers be crammed together when there are open seats on the flight?
A : Please try to understand.The problem is that if we gave you the seat,it wouldn't be fair to other passengers who might also want the open seat.
B : That's a drag.Especially since U requested a window seat at the front of the plane/and they put me on the aisle near the back!