Originally Posted by metallo

It's completely unprofessional. I would never advocate for someone to be fired or even formally disciplined otherwise for something like this (perhaps he was simply fed up after some recent incident with a passenger and was blowing off steam).

However, the airline, or perhaps even just his peers, should strongly advise him not to repeat this behavior, in my opinion. Paying customers, most of whom are adults, shouldn't be lectured in this manner.