I did it last night with a cashier and she laughed and was, I think, amused by the novel response. It seemed to brighten her up a small amount. She then continued to make conversation by saying “Well let’s see if we can’t get you to better than normal.” That was slightly offputting and I wish she didn’t feel the need to take it there. I’m perfectly content with feeling “normal”.
I suppose the way I think of it is like dynamic range of expression. Normal is baseline and perfectly suitable. It’s where I like being. Great or bad are for special cases where I feel extraordinary.
-- What, "can't complain"? Really? You're in a Siberian prison camp, starving and freezing your toes and fingers off, and you "can't complain"?
-- Yes, when you're in a Siberian prison camp, you can't complain...
But it might be one way to start a conversation when you want to tell something you don't like. Like "How are you? I'll live. What happened? ...". But it's more of closed friends conversation when you can feel OK sharing your burdens with other person. I guess, similar thing could happen in US?