A phrase used to describe someone who is sexually attractive because of their high IQ or because the way they think is unique or seems very similar to the attractee's own ideals.
"He has a PhD in psychiatry & neuroscience and works for Doctors Without Borders. He doesn't look like much, but damn, he's got a sexy brain."

"I love her sexy brain! It's like she knows what I'm thinking before I do."

Some examples of famous sexy brains: Pierre Elliot Trudeau, Dr. Ruth Westheimer, John Stewart, Jodie Foster, Barrack Obama, Oprah Winfrey, Steve Jobs, Ayn Rand
by Anemonii February 4, 2010
When you have a sexy brain, you're extremely smart to the point where people want to sleep with you because of it. A brain can be the sexiest body part if you train it to be that way
by GOD517 April 21, 2018
Literally Joe Jacob Rogers from England.
I’m so smart literally a sexy brain.
My noggin is huge I’m a sexy brain honestly.
by Sexy Underage Kitten August 31, 2021