Princes face wen he says it lol
Pinky was the genious
1) Brain comes up with a plan; 2) Pinky makes a relevant observation, but Brain ignores it; and 3) Pinky turns out to be right, Brain fails. In the second episode, for example, Brain builds a robotic suit to compete on a Jeopardy!-style game show, but loses by not knowing an answer to a question Pinky had answered correctly. Also, the same episode demonstrated that Pinky can read while Brain is barely able to write his own name
But the most conclusive evidence comes from the episode "That Smarts," in which Brain uses a calculation to identify what makes his plans fail. And the machine says its pinky...
So Brain creates a "smart machine" to turn Pinky into a genius ... but his personality doesn't change in the least (which should be our first clue that he was intelligent all along). Smart Pinky then points out that Brain made an error in his calculations, and the real reason his plans fail is this:
At the end of the episode, Pinky goes back to being dumb ... or pretending to. It's clear to us that Brain's machine never worked, just like most of his inventions, and Pinky simply took this opportunity to reveal his real self to Brain for a while.