If you encounter many miserable and bitter people, you are probably not so positive and happy yourself.
Let's face it, hundreds of people in a metal tube is not exactly a positive environment for the most part. The majority of people will be miserable because most don't like to not have control. If you go in with a negative attitude, that's what you'll get.
Oh, and misery is not limited to Flight Attendants. Singling them out is very common. Expectations are high for passengers for some odd reason. Odd because this is 2010. Long gone are the days of Stewardesses shaking their tails for you, and handing out cocktails while you sit there in a business suit.
People want cheap fares, but have high expectations of what they get. It's the world we live in.