A while ago, I was involved with a group that was practicing a martial art, and had regular practice sessions in the evening. It's not really important which one, what is important to this short story was that I was a stranger to all these people, and that never really changed. And folks were from all parts of the world, with a particularly large proportion hailing from the UK or other Commonwealth countries. So they tended to be polite, and there were rote things they'd say like "good evening, how are you?" Like the complete nerd/social ret*d that I am, I would put some thought into my responses and answer explicitly, taking up at least 45 more seconds of time than the 2 seconds that the greeter had in mind.
After a few weeks of this, one fella took me aside for a bit and, really nicely, explained, "You know, when someone asks you how you are, you should just say 'fine.' Because in general, unless you have specific information otherwise, well... if you're not actually fine, the person asking probably doesn't actually want to know." He had to point it out to me for me to realize that, yeah, he's probably right. It'd be rude for him to not say *something* if it's the first time he sees me that day, but it's also sort-of rude for me to take up more than a few seconds of his time for me to also acknowledge that he's nearby too.
It took me even longer to realize that, yeah, having to have this explained to oneself at 25 years of age is probably ... atypical.