I just tried to do this balance thing that apparently only girl can do and couldn't do it. My brother laughed and said "Ha! You're not a girl!" His insult backfired because it made me feel better lol.
The balance thing said it for you :') I'm sorry now, but whatever you say, for all of your life, you won't be allowed to be a girl. This is a rule, you didn't arrive to the balance thing you're not a girl. Your brother knows that.