I had an insufferable coworker who doubled down on that attitude. If he hadn't thought of something, instead of just saying he could have done it, he'd start rambling about why it was a bad idea, and that he was smart for choosing not to do it. His whole attitude was "I know everything, and if I don't know it, it's because it's not worth knowing". Worst part was the non-technical management ate it up because he was so confidently wrong, so people got dragged into working on his convuluted solutions that just happened to always match up with his skillset.
I have to deal with a couple of people like this and it's a waking nightmare. I'm trying to figure out if it's even possible to mitigate their damage or successfully negotiate with them, or if I just need to change jobs. This behavior is especially bad when it comes from manager / team lead types.
Or by adult professionals on Hacker News.