A special title, and there are two most important uses of the title:

1. If your girlfriend is calling you this, smile or laugh and call her Wise Girl. She would love it, and love you more.

2. If anyone else calls you that, feel free to call him/ her any names you want, though it's best to call them "Pinecone face".
Gf: "Hey Seaweed Brain!"
Me: *smiles* "Hey Wise Girl!"

Random Guy: "Yo Seaweed Brain!"
Me: "Don't ever, EVER, call me that again, Pinecone Face!"
by Percy Jackson fan101 April 29, 2018
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Sex term used when two best friends are both in relationships; however, they definitely fucked in a closet one time. One probably has had red hair at some point in their life.
"My two best friends are for sure Seaweed Brains" spoken by a very intelligent and charismatic man who is named after an angel from the bible... probably.
by Gazil Backstreet February 16, 2022
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it means, you are an idiot, and you are reading to much percy jackson books
hey brian, hey, guess what, what, your are a seaweed brain
by andrew17 November 23, 2010
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