DEAR MISS MANNERS: I am the third daughter in a family of seven children — six daughters and one son, with my brother being the youngest. Anytime it is disclosed that my brother was the last child born, someone will say something along the lines of, “Wow, they must have really wanted that boy!” I understand that people think they are just making conversation, but it is crass at best, and increasingly insulting as one goes down the line of girls who had to be “tolerated” in order to get the golden son. This used to infuriate my father so much that he started replying, “No, I just really love t…