"hey, your...."

It seems like being the youngest child of your family has many many perks, but at the same time there is one thing you hear ALL the time.
I thought this would eventually go away, but guess what? It doesn't.
The statement: "Hey, you are Matt/Sandi's sister."
I mean, I don't mind it, but it can get old. Ever since I could remember I have gotten it, especially in elementary school. All I want to do is say, "No, really?? Because I didn't know that!" I'm sorry. Sarcasm is just in my blood.
Haha. Please do excuse this post.