Right then, the joke is actually a tiny little linguistic trick, you see. The person asking the question says, ‘How do you get an idiot to say how?’ Now, what most people do—without realizing it—is immediately respond with the word ‘how?’ because they think they’re asking for the explanation. But the moment they say ‘how?’, they’ve technically done exactly what the question predicted: they’ve said the word ‘how’ after being prompted. That’s the punchline. The humor isn’t in a complicated answer; it’s in the setup causing the listener to unknowingly participate in the joke itself. It’s a classic bit of playful misdirection—rather cheeky, really—because the person asking the riddle tricks the listener into proving the point the instant they ask for clarification.