1. a keen mind, formidable intellect

2. that which an intelligent person uses to predict future events instead of a "crystal ball"

This term was coined by comedian Adam Carolla on his morning radio show to combat a harpy lawyer who was insisting that she couldn't possibly predict what an obvious outcome would be because she didn't have a crystal ball.
Reasonable Person: That new Sandler movie is gonna blow ass.

Douchebag: You don't know that. You don't have a crystal ball.

Reasonable Person: I don't need a crystal ball; I have a crystal brain.
by ContusorOssis November 6, 2012
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A person that's so much of an idiot that you could actually see through their brain, and of course there is no brain cells.
John: I just broke your cat's leg for fun!
Miranda: You fucking crystal brain, you're so fucking stupid that everyone, even the stupid know you're stupid
by LoogieSolos April 3, 2022
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