In Malaysia, I'm not sure what's the right answer for questions like "how are you" or "how's your day". I think Westerners see them as a form of small talk, so the answer is always 'good' or 'fine'. They only expect a reply, but they don't care what you answer. Just like how we are taught in schools, for "How are you?", the reply is always "I'm fine. Thank you."
But many Malaysians see it like a real question and answer it by telling how they have not been good, how they've been busy etc. The grammar nazi in me feels like standing out to correct them, but I always brush it off. And it's become so common among the people I talk to to the point that my responses like "I'm fine" are odd to them.
I'm still undecided whether this should be considered a register or simply bad command of English among the people I talk to, but I'll just stick with "I'm fine, thank you."