On polite insults

<Student asks a very obvious question.>
“You’re not smart.”
“That’s rude!”
“Yeah, let’s not insult each other.”
“Or at least do it politely.”
“That was polite, at least I didn’t call you stupid.”
“No, a polite way to insult me would be to say, ‘You’re not the sharpest spoon in the drawer.'”
“I’m sorry, Miss.”