I don't exactly hate it, but it really puzzles me when I'm in the US and at every shop the staff asks "How are you today?" I am never sure what I am expected to say. I'm aware that it's just a phrase but would it be acceptable for me to speak the truth (not that well, I have a horrible headache, but thanks for asking) or am I expected to follow the hollowed American tradition of white lies and say "thanks, I'm fine" even when I'm on the verge of dying?
I don't know about the rest of the buisness world, but at the small chiropractic office where I work we are told to ask "how are you today" as a way of making the patient feel welcome. As for the "appropriate" response, there isn't one. Whether they say I feel awful or just fine is up to them. Of course thats for a health care facility. I have no idea how someone in a grocery store would expect the customer to answer...