It is so simple, yet so brilliantly diabolical. Whenever somebody says anything, just respond with, "I know." You may be thinking that this is stupid and makes no sense, and you would be correct on the former but incorrect on the latter. It makes perfect sense. After somebody tells you something, you gain that knowledge. You're not saying you knew that, you're saying you now know that. Here's an example:
Random Holiday Person: Little Billy is starting to read.
Me: I know.
RHP: How'd you know that?
Me: You literally just told me.
Feel free to follow up that by looking around with a face that asks, "Who is this clown?" to really hammer your point home.
Everyone will hate you.
And isn't that what the holidays are all about?