Oh Shanks, you are so right--It is such a lazy habit, for people to think that they can "know" your by fitting you into a neat little category.
It is one of my failings--I keep thinking I have gotten over its, and they some one will say something, and I realize that I have a stereotyped someone by their age, ethic background, religion, haircolor, or some other meaningless attribute. Not always negatively, but stereotyped them none the less.
A english gentleman once put a very large foot in his mouth when he asked about my background (he was surprised at my knowledge of "english" English, and when I replied I was Irish American, the words "But your intelligent!" fell out of his mouth. It is very unpleasant to find yourself stereotyped! I am always vaguely aware that the irish are not always held in high regard, not even here in US, but it rare to come face to face with it.
