I tried "not great" once. The other person looked so alarmed that I spent the next two minutes reassuring them. Never again, probably.
answering how are you on a bad day
someone once said "no, really, how are you" and i panicked and told the truth. nothing else about the conversation changed, i just kept thinking about it for a week.
"yeah, good, you?" i've said it on some really bad days. not exactly a lie, i just never get asked again after that.