we'll cross the rats-deserving-to-have-"duh"-said-to-them bridge when we get to it

Sage: "Have you seen 'Colly the Plant Murderer'?"

Eric: "No, I haven't. Did you just make that up?"

Sage: "Yeah. Duh."

Eric: "Don't say 'duh'! That's not nice."

Sage: "Can I say it to a bully?"

Eric: "No. Don't say 'duh' to anybody."

Sage: "Can I say it to rats?"

Eric: "No. Rats never did anything to you."

Sage: "What if they do?"

Eric: "And that's the end of this conversation."