King of the Classroom

Listen up, buttercup. This is a pun, see? A "ruler" is a thing you use to draw straight lines. But "ruler" also sounds like "ruler", as in a king or queen. So the joke is that a ruler is the king of the classroom because it's a ruler! Now, I know you're probably still scratching your head, but don't worry. You'll get there eventually. You're a special kind of person, you know?