There is no single brainiest person. The universe doesn’t work that way. You’ve got chess grandmasters who can’t open a bank account, and you’ve got farmers who can predict the weather with 99% accuracy by sniffing the wind.
The real brainiest person might be the one who knows they don’t know everything. That’s called humility, and it’s the smartest thing you can have. Would you rather be the guy who memorizes pi to 10,000 digits or the one who remembers to call their grandma on her birthday? Case closed.
Final brain fart: The next time someone asks you this question, just point at the nearest cat. They’ve been manipulating humans for 4,000 years. If that’s not genius, I don’t know what is.