How do I get him to stop treating me like this?

So there is this guy that used to be in my cl all through grade school (came to our school in grade 4) and a few cles throughout highschool. I liked him forever and I know he liked me at times also. I was always really shy though and would not say much when he would talk to me. Everyone knew me as the cute little pretty quiet girl. I'm not like that anyomore and have grown up and grown out of my quietness. How do I go about showing this to him? I will be going to a banquet supper and he will be there. Last time I saw him he treated me like he used to like "omg did u just tell me to shut up" or little childish talk like that. What can I say or do to just get him to act normal around me? I'm 17 btw