So sexist!!

There is a kid at my school and I am kinda a feminist and his mom is a teacher at the school.I wore a shirt that said “girls can do amazing things.”and he had the nerve to tap me on the shoulder and tell me “no they can’t”so at this point I hadn’t lost my cool,yet.So I tell him you’re being sexist and he said “no I’m not” I asked if he knew what sexist meant and he does then later he said “it was just a joke if you don’t have a sense of humor it’s not my fault”how is that funny?!