I think it's really subjective. When you already are in the bad mood (time zone change, family problems, bad attitudes, long day meeting etc as other poster named them), you would be still mad even if you heard the nicest thing in the world.

Sometimes being a DM makes your expectation goes unreasonably higher (I myself sometimes has that feeling too). I have never had those kind of experiences yet which makes it hard to believe for me. However, I am also aware that when you choose to be in Y, I'd know how to deal with my expectation i.e. not getting mad (and perhaps speak harshly to the check in lady) when I don't get an op-up or seat blocks when the flight is full