My younger brother is better endowed, now he won't stop bragging?

I'm 19 and my brother is 16. He would always say he thought he was better endowed than me, so I had enough and said "Let's see then". Well, it turns out he was right, he laughed and rubbed it in my face. He always brings it up and won't let me forget it, what should I do?
My younger brother is better endowed, now he won't stop bragging?
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