The best answer I ever heard a speaker give during a post-talk Q&A session was at an AI conference back in the day. I was a grad student, and the speaker was a professor from our CS department — a smart, mild-mannered, friendly guy.
The question from the floor was complicated, and somewhat irate — it involved several references to other under-cited and related sources, and called the speaker to account for subtle biases revealed by certain subsections of his talk.
The speaker replied in a friendly and mild-mannered tone, in a single sentence, and then moved on to the next question. I wasn’t sure I had heard the one-sentence answer correctly, and afterwards tried to confirm it with my friends who were there. Everyone had heard it the same way, and felt the same need to confirm. (We later confirmed it with the speaker himself.)
Want to know what the answer was? It was: “Your work has driven you mad.”
Tim Converse 
Am I allowed to ask if it’s who I’m thinking of? It’s the “mild-mannered” and “friendly” part that makes me wonder…
It’s probably not who you’re thinking of. 🙂
Indeed, I showed this to Jim, and he denied responsibility.
It is, I agree, a great answer. I don’t think I’d be able to pull that off.
The last name begins with the letter ‘O’.