I Kant.
Explanation: This joke is a pun based on the name of Immanuel Kant, a central figure in modern philosophy. The humor comes from the wordplay on “Kant,” which sounds like “can’t,” making the speaker’s response both a refusal (“I can’t”) and a clever reference to the famous philosopher. The joke works because Kant’s complex and challenging ideas are often difficult to explain, so the response feels appropriate while also delivering a play on words.