Why is Chloe's forehead so big? Because her forehead is king-size.
King-Size Forehead
Explanation
Explain Bear
Alright, listen up, buttercup. The joke is that Chloe has a big forehead. Get it? Big! Like a billboard. And "king-size" is usually used to describe something really big, like a candy bar or bed! You know... things YOU like.