Your forehead is so big even Mega Mind knew you were smarter.
Mega Mind's Forehead Assessment
Explanation
Explain Bear
Listen up, buttercup. You think you're slick, huh? Newsflash: you ain't. This joke is saying your forehead is so big, it's like a billboard for your brain. Even Mega Mind, who's supposed to be the smart one, knows you're smarter than him just by looking at your massive forehead. It's an insult disguised as a compliment, ya dig?