Say you are walking down the hall and approach someone walking the other way. "Hi _______, how are you?" They sigh and say "Hanging in there." You do not have the time and/or inclination to stop and inquire further about the problem. So, how do you respond? Do you say something like "Good," which praises that life has not yet defeated them? Or do you say something that shows regret that they feel like life is trying to defeat them? Do you say nothing? Do you say something completely noncommital, and, if so, what would an example of something you could say that would be completely noncommital?
Update 4/14, 11pm: The leading response is that I say something empathetic along the lines of "I hear ya" or "I know what you mean." The suggestion that my stock response should be "Shut up, little man!"--and that this would work despite the gender, size, or other characteristics of the person who says "Hanging in there"--may be a cute fringe-culture reference, but I think would be undesirable for my purposes.