If both pilots were out of the cockpit this needs to be reported - ASAP, dangerous, stupid, arrogant and I'm sure that the FAA would be very interested.

As an aside (and this may not be current now) but it used to be aviation law that, where two pilots are required and one has to 'leave' the remaining one must also put on his / her mask in the case of emergency being the only pilot present. Also why male pilots are not allowed to have beards (they interfere with face masks apparantly).

Anyhoo - I digress, certainly write to Iberia for their 'feedback' and take it from there.