I really wish I could be one of those 'good mood' people.  I wish I could hide my emotions better, or at all.  For my entire childhood, adolescence and teenage years I was great at it.  As I've gotten older that switch just doesn't work anymore.  It has gotten me into many an unpleasant situation but it has also earned me a lot of respect in that I don't pull my punches and will say what is on my mind. 
Right now I'm in a very stressful situation that shouldn't be that way.  I cannot go into any detail but I can say this, if someone bails your butt out of a really bad situation and gives you yet another chance to make good on your life you really should not disrespect their home and their wishes. 
In previous dealings with hard to deal with people (never go into business with 'friends'), a simple Thank You can go a really long way.