I sometimes encounter a different version of the Captain Know It All and that's someone who serves up a fact about something and gets offended when you already know about it. I have a relative who does this a lot. "Say, did you know that the Earth revolves around the sun?!" And when I say that I did know that, they get pouty about it, like how DARE I know that?
?. It is so bizarre.
Maybe that should go in the brain hurt thread...
I'd love it if DH would just pout when he pulls that one. Nope. I say "yes, I do know that" and he ignores me and proceeds to expound on the subject until I'm ready to puncture my eardrums just to make him stop!
SS Relative (SSR) is one of these, also. Months ago, I made an innocuous statement for my FB status, "Enjoying beverage w/blankety-blank made by my wonderful DF." SSR then took it upon herself to respond, "Do you know that blankety-blank isn't vegan? It's made with blah-blah that comes from animals!"

was my immediate thought since I'm not vegan, never have been and never professed to be. However, this was not the first idiotic post SSR has made, including to *my* FB page so I simply responded with something like, "Hmm, I'm not vegan. However, I've known blah-blah is an animal byproduct and have known this for about 30 years; haven't you?"
Anyway, she never responded to that but, apparently, she counted it as one of my many "offenses" against her and when she tried to force me to address said offenses (sorry, but unless she were willing to have a two-way convo where I'd get to speak my piece, also, about the offenses she committed, it wasn't going to happen), she did me the great relief of not only dropping out of my wedding (she was supposed to be a bridesmaid) but also not attending (both of which is actually what I wanted -- her dropping out and not attending -- after experiencing her increasingly obnoxious behavior, not limited to e-mailing then-DF to make him make ME deal with her issues with me and publicly posting on our FB wedding page how terrible our wedding menu is -- yup, that's a person that really needed to be a part of our wedding day!). Apparently, she still posts CKIA stuff on her FB page. I think the rest of us just go "okay, whatever" and move on (well, those who still see her posts; I blocked her updates from my newsfeed a long time ago since they were just too nutty and numerous).