"Churlish" is an excellent word for this. And my response to this is definitely colored by the fact that "someone being a grouch to you isn't your fault, but it means they want you to leave them alone" is a lesson I was taught via uncles (who in retrospect probably have veteran-related trauma issues) at large family gatherings at that age, that has served me well in later life!

Meanwhile I am currently dealing with a coworker who thinks the correct response to a customer saying "I can't do this right now" and walking away is to follow them and keep talking, and doesn't understand why this goes poorly for her, so the importance of that lesson is much on my mind!