I can't believe that some of those guys have actually the responsability of flying an aircraft, and here they are talking about food (and water), simply amazing.
I must say, I have never ever came across any of those guys, (the demanding ones), maybe because I always made it clear what was available and when it was available and thigs were arranged from the begining of the flight. You do hear some of those stories but the cabin crew plays a big role in it and surely can help in giving this guys an alternative meal if the desired choice is not available.
I also must say that they have always been very flexible in term of cockpit visits and rest, so why not make an effort on the cabin crew side and at least try to arrange something decent and apetizing for them?, "one hand wash the other" and believe me that they are the most amazing people and the ones that will stand up for you when an emergency or a problem happens.
I think that the crew should not pay much attention to those comments and simply try to get along keeping the conversation flow at all times.
Happy flying !!!!