Just to get it out of the way, social anxiety and introversion are two different things that don't automatically come in a pair.
With that out of the way, absolutely I used to get it all the time. A few examples: expressing my feelings on a rare occasion- "Oh my god, you have feelings?", a girl at a party asks the host to get a spoon for me- "Well, why don't YOU ask me? Do I make you uncomfortable? HUH?", a girl in my grade asking me a question and then walks away- "Oh my god, why are you so red? You go red whenever anyone but [our group of friends] talks to you!". Just along with the generic "Why are you so quiet?", "Why do you never talk?" etc.
You just have to shake it off, really. The people who usually ask you are the ones who socializing comes naturally too. It's so normal and natural to them that they don't understand why anyone else would be different- sort of the same reason why quiet people don't really understand why some people never stop talking (except they are the majority and so, we don't ask). Most of the time, there's no cruel intent. They just want you to be happy and talkative like them. I did however have a friend (who I cut off as a result of this) who I admitted I had social anxiety and she actually laughed at me when I almost had an anxiety attack around a teacher who major set off my anxiety. She intensified the whole situation to the point where I had to get up and leave. Normally I wouldn't do that because that in itself is embarrassing, but in this situation it was the lesser of two evils.
Anyway, I'm going on a rant but really, you just have to shake it off. It's usually not personal, it's just because they don't understand. When it is personal, cut that person off. They don't deserve to know what you think about. You will get a lot of this in your life and it's better to learn how to deal with it now rather than later. x
