I didn't mean to offend...really??

So we are talking down Fayetteville Street in downtown Raleigh, enjoying a sunny (albeit hot) Saturday afternoon, and admiring some gorgeous classic cars.  Not that I would have wanted to live as a woman in the 1950s, but man, some of those Bel Air cars were stunning.  The shiny chrome, deep red paint, and pristine leather seats!  Stunning.  Although I am not sure how a 1986 Z28 Camaro can be considered "classic" in the pure sense of the word - it was a lot of fun.  As we were walking along minding our own business, I took a turn with Christopher down one of the side streets.  As we were strolling along, a man who was standing near one of his cars points at me and yells "Chinese?"  I try and pretend I didn't hear him and just shook my head.  He then says "Korean?"  I could of said, Yes, but instead, because I am who I am, I yell back "American!"  He looks visibly disappointed, and replies, "aw, I was hoping to try out my Asian on you."  At that point, Scott, my usually quiet mate comes up behinds me and says, "so, what are you, huh?, German, English, Irish?" The man then looks totally mortified and as he turns to walk away he says, "sorry, didn't mean to offend."  Didn't mean to offend.  What do these people who say these insensitive, ignorant or just idiotic things think is going to happen at the end of that sentence?  I am a STRANGER!  I do not KNOW YOU!  Why would you think that is OK, under any circumstances?  I am almost tempted to create a T shirt (as I was taught how to do by my cool friend SJ) that says in big, letters - DO NOT ASK ME IF I AM Chinese, Japanese, or Korean.  You will not like the answer.