The worst thing you can do is what I have just done: condescend to CG. He really hates that and will explain things to you with even more earnestness. NEVER engage in debate with CG. It is not that he will "win" the debate, but that he will drag you down to his level. He will win just be having you take him more seriously than he deserves.

I should point out that YOU, dear reader, are not Condescending Guy. If you recognize him in yourself you are wrong. In fact, you can take comfort in the thought that, however, much of a CG you are, I am probably much more of a CG than you could possibly dream of being.