Personally I don't tell people the truth as I think when people ask, "How are you?" they don't really want to know. For most this greeting is no more than a cultural expectation. Sometimes when I'm bored I'll answer with something like, "I'm dead inside" when an unsuspecting cashier asks how I am. It's funny because most ignore it, but once in a while someone will just about panic. It's a cruel hobby, but i enjoy it.

With my closest of friends I will tell them something like, "I'm in a rotten mood," if they ask when I'm having one of my moments, but i don't get into depth with them. I probably should. I'm a total nutcase.