Just taking the time to listen to their complaints the whole way through with out butting in (which can be very hard to do sometimes), and a sympathetic nod of the head with an "Mmmm" thrown in here and there. Usually does the trick.
Sometimes people just want to get it all of their chest and when they feel that you have really listened to them and shown a bit of empathy (they dont have to know that you might think they are a t**t) then it usuallys calms down and gets them on side. It works for me anyway, i've had many apologys from pax after they have had a rant.
However ther are a minority of people out there who will always love to be rude for no reason and unfortunately nothing anyone does will pacify them
