Yeah, that's pretty typical. Usually it's the vacuous stare and the "oh... well, what's that?". I have found that advanced planning is easier to explain than current planning.
Whenever I would explain current planning (reviewing proposed developments for conformance with city bylaws, policies, etc... making sure that developments don't harm the environment, etc...) I would usually get the following response: "so you are the one that reviews plans and then inspects buildings to make sure they are safe?" Depending on who it is I am talking to, sometimes I would just be like "yeah, sure"... if I actually thought this person cared about what I do, then I would go through the process of truly explaining it (maybe I've been through this too many times and I've gotten sick of explaining it over and over).
My father went to some business function recently and met some colleague's daughter who had just graduated from UCLA's planning program. When she said that she started work as a city planner, he replied that I had been working in the field for many years. Her response: "Thank God I don't have to explain what I do for once!" So I guess it really is universal.