Confusing greeting issue...

I've come to realize that I don't really understand the greeting 'how you doin'/heyhayadoin'?' It would seem that this form of address means different things to different demographics. To me, when someone asks me how I am, I always say 'fine/good,' and return the question to the asker. This works all right in certain circumstances, usually older ladies who appreciate courtesy and often carry the conversation further, but in others it falls flat. When walking past a middle-aged or older males, 'heyhayadoin?' seems to be more of a greeting than an actual inquiry about how I am; when I say 'fine, you?' these gentlemen usually keep walking brusquely by like I somehow dropped the ball and dragged the interaction further than it needed to go. When walking by younger males, 'how you doin?,' when answered by 'I'm good, you?' makes me feel like the worlds biggest square; clearly here, as well, it's meant just to be an acknowledgment of some sort - I'm not very cool, so I don't get it. It's a moot point when dealing with younger females of any demographic because they always speed up as they pass me by, and avoid my smile; I guess here I'm still seen as competition, so contact is to be avoided at all costs. Other demographics break off into their own forms of acknowledgment that aren't nearly as lodged in the gray area where 'how you doin'/heyhayadoin'?' lives. Life would be so much more simple if everyone stuck to the nod.