How do you respond to someone who confuses your gender?

Last Friday, a speaker from the Republican party came to my high school and gave a speech on why he worked for the Republican party and what his daily schedule consisted of during an election year. After he gave the speech, the audience was allowed to ask questions. I raised my hand knowing he was sexist, because before the Q&A session he said, “now girls will need to speak louder, because I have trouble hearing girls”. However, when I raised my hand he told me “I will answer your question in a minute young sir” and answered the boy with the Sarah Palin button’s question first. When he got back to me, he continued to call me “young sir” until I told him “actually I am a woman”. The look on his face was priceless! But I was hurt by his comments.(the entire school saw this conversation) I do not want to be called “sir” until I get knighted!
I am proud to be a woman even if I don’t look “stereotypically female” and comments like that are a slap in the face. I hate it when people call my gender into question! Yes, I could conform, but that is not me either! I am a woman, a woman that doesn’t wear makeup or pluck her eyebrows or wear “girly” clothes, but I still LOVE the fact that I am female!
I guess my main question is, what is the best way to remain calm when someone calls your gender into question when you don’t want it to be called into question?