For me the biggest is Jojo. Yes I know, I have pretty much no excuse for not yet at least watching the anime (first three parts are already done and part 4 just started), though in my defense regarding "the mango," I've heard some parts don't have very good translations yet (I keep hearing that the reason part 5 isn't as liked in the West as it is in Japan is because one of the only English translations available is not very good).
Even so, there's still a decent amount of stuff about Jojo I know about simply through being around fans a lot online, be it the names of some of the protagonists and their Stands, knowing that Stands only became a thing starting with part 3 and that something called "Hamon" was the "main power" in the first two parts, Dio is by far the most popular antagonist of the series and his son is the main character of part 5, the protagonist of part 8 shares a name with the protagonist of part 4 (and part 8's protagonist has "Gappy" as a popular nickname), there's a character named "Funny Valentine" whose Stand name got altered in the English version of one of the Jojo games because the Stand is named after an AC/DC song and the publisher didn't wanna risk getting sued (and Funny Valentine looks like Arin Hanson/Egoraptor sometimes), and so on.
I know all this random information in spite of never seeing or reading Jojo, mostly thanks to "fandom osmosis."