me_irl

If it's a short interaction, I'd rather just exchange meaningless pleasantries to indicate to them I'm a normal person and we can both go about our days. I don't necessarily want to talk to them at all, but saying, "hey how's it going" "fine, how are you" takes no effort and lets both parties quickly evaluate the mental and emotional state of the other. It's social lubricant, it's more hygenic than shaking strangers' hands and quicker than telling them your life story. Plus if it's someone doing their job, I'm not going to try to start a substantive conversation with them, that might just distract them and cause them to make a mistake.