Can I ask my brother to leave my childhood nickname out of his speech?

My brother sent me the opening of his speech for my graduation dinner: "We never thought little Disaster would get here." Disaster was the nickname he gave me after I broke a cake stand when I was nine. I'm thirty now, and I've asked him twice in the past year to stop using it around my friends.

I replied that I loved the bit about us revising at the kitchen table, but wanted the nickname and that first line removed. He said, "It's affectionate. You used to laugh." He's right that I did. Sometimes it was funny, and sometimes laughing was easier than explaining why I hated it.

He helped me practise my final presentation and is proud of me. I asked him to speak because I wanted that history in the room. I don't want to replace him over one sentence, but I don't want to spend the dinner smiling through an introduction that makes me feel nine again.

How firmly can I put this without turning the whole speech into something he has to submit for approval?