What have you just found about that you had no idea existed, never even considered it, but now that you know you can never forget?
Here’s a start: Dinosaur porn.
What else ya got, folks?
…I was not ready for that example.
Dang! I was gonna say “Glitter polish” but that pales in comparison.
Those parasites that replace the tongue of their host.
And, by the way, I am SO happy to not click on the OP’s link…
FTR, the two-click rule is observed.
Decorative and ornamental onions are apparently a thing. Alliums.
Grape pie.
Another vote for grape pie (but now I want it).
Dark matter.
Biscuits and gravy. I’m pretty sure I first learned of their existence via this board.
Edit: I should add that, as an Englishman, I was fully aware of biscuits, and of gravy, but not in the sense of things that belong on one plate.
Intelligent people on the Internet. 
Furries.
This is almost embarrassing but the first time someone served me Seedless Watermelon, I had literally no idea such a thing existed. I found it amazing. It was like I was the apes in 2001 A Space Odyssey
It’s been a few years now, but anal bleaching. Never occurred to me that anyone would want or need to do that to themselves, or that they would pay good money to have it done. 
Yet another vote for grape pie.
I’m routinely amazed by the modern world. I’ve been experiencing future shock intermittently since the first time I burned a CD.
As for Dinosaur Porn, that’s covered under Rule 34.
Lifelong baseball fan. Never knew that each clubhouse has a guy who dirties up baseballs before games until I read this article earlier this year. They’re rubbed with special dirt even.
^^^ there’s an episode of Dirty Jobs about harvesting the special mud.
How coincidental! There was a show last night on interesting jobs and one of them was the guy who provided the specific mud for scuffing baseballs. Evidently, the mud comes from where a river is near the Atlantic in New Jersey and has a high content of an element I want to say was quartzite, but could have been something similar. Evidently, he learned the source of this mud from his father who learned from his father. He ships some 800 pounds of this mud to various teams per year.
The Sentinelese of the Andaman Islands who have aggressively resisted all contact with civilisation. An untouched people - I hadn’t realised there were any left on the planet.