Strong customer service is crucial to the success of an airline. Discuss with the interviewer how you would deal with this type of situation. If you have experienced this before, use a real-life example.
"My reaction would be different depending on if the colleague was one of my direct reports or not. If the individual reported to me, I would speak with them about the situation in private and request that an apology be granted. If possible, I would upgrade the passenger on their flight seating as well. If the colleague was an equal I would likely leave it be and just take special care and attention on the flight to make the passenger feel comfortable and welcome. If the situation became a common occurrence I would bring it up with management."
"I'd approach him in the galley and chat him up, see if there's anything that's bothering him that might affecting his attitude. Maybe he had a fight with a friend or family member and he didn't leave his personal baggage when he came in to work. If that's the case, then I'll try to let him vent a little bit with me, and then encourage him to focus on something positive. Then I'd suggest to him that the passenger he was rude to looks a little upset at something and that he should check in with him. That way the passenger gets a taste of my colleague's more positive attitude."