<font face="Verdana, Arial, Helvetica, sans-serif" size="2">Originally posted by gleff:
Perhaps F was oversold. The person who wasn't on the plane had a revenue F ticket but no seat assignment. So they had more people assigned to F than seats, and they had to downgrade someone.
</font>
The person who was downgraded was the companion that must have been cleared by the gate agent. I doubt the gate agent would have done something like it if the flight was oversold.
I believe this is a case of bad judgement by the gate agent, both in upgrading and then in handling the situation. If the agent did not give any explanation, that's a reason to complain about.
However, when complaining - expect an answer like - you did not pay 1st class so you do not deserve any compensation for not flying 1st class.