I was taught years ago to say howdy to everyone and to say it with something resembling a smile. And when driving to give a polite wave at just about everyone.
It's so ingrained in me by now that I would really have to fight myself not to say howdy. I even regularly say hello to dogs, cats, horses, cattle, ..., and I often wave at them while driving. And around here, nearly everyone says hello or waves back whether you said hello or waved at them or not.
It's all about trying to fit in and be accepted.