Do you know of a crazed fan of something/someone in real life, and if so, what are they like?

I'm not talking about your average (or even slightly above average) fan of something where they spend a lot of money on concerts and merch, I'm talking unhinged, gets into days long fights online, waits for hours at the airport (idk maybe this is pretty normal for kpop fans), Club Chalamet-level stans.

For me personally, the worst I've heard is a colleague of my aunt who used to go on car chases stalking kpop trainees and spend all her salary on taxis back in the 90s, and of course, Club Chalamet's nonsense. And the black mold BTS fan?

I wanna know if people here know people IRL who secretly or not so secretly are unhinged fans of someone or something to the point where it's concerning and also how it seems to affect their lives!