how to brush it off?

This guy and I are 21. Recently, he's at the beach with his friends and some girls are there. He keeps telling me that this one girl kept saying I look like dory. I mean I'm a girl, so of course I'm slightly offended. Like stop making fun of my appearance. So I blocked him from texting me.
How do you handle insults and Not get offended? I'm so insecure about my looks and need help.
Edit because I would like to remain anonymous. Yes he was technically also making fun of me because he also called me dory and sent a picture of me and of dory to compare ourself. Writing this out makes it sound really silly. 

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