I’ve always been confused about how to handle this situation, and it happens mainly in relation to my family members. For example, I’ll be at a grocery store, and I’ll run into someone who knows me and my parents. After we exchange pleasantries, they’ll say something like “Tell you mom I say hello!” Should I take that literally and tell my mom that person says hello or is it one of those weird social things where people tell you do something, but you don’t really do it?
In the US, certain things are ritual greetings that follow a standard script. Deviating from it is considered a bit weird (but it’s also common, and possible to get away with. I deviate from it often).
“How are you?” is not usually intended as a real question. The expected answer is along the lines of “Fine, and you?”
The default answer to “what’s up?” is something like “nothing”, or “Not too much; yourself?”. It’s considered slightly less weird to answer