There's something of a running joke on r/anime that, when a user asks for a recommendation to introduce a parent/work colleague/friend to the medium, someone will suggest School Days.
Based on a visual novel, the show follows a high school student's attempts to woo a girl he sees on the train to school every day, with the help of a classmate. This setup lasts for all of an episode before things take a turn for the complicated, and the series ends with the most… unconventional resolutions to a love triangle.
Makoto Itou is, in short, a total asshole. Initially (mostly) relatable, he quickly embraces his inner sociopath as he fucks his way around the student body, seducing (sort of) a series of female students, driving away his girlfriend, and eventually being brutally stabbed to death by a classmate pregnant with his child.
I just finished watching this show an hour ago, having started it this morning, and I'm still processing a lot of it - and I knew how it ended ahead of time. If I'd been going into the show unprepared, I don't know how shell-shocked I'd be right now.
Right up to the end, there's a lot of visual and musical cues that you'd expect to see in a romantic comedy anime, even as characters literally lose their minds. It's like the whole thing is set up to make you believe there's going to be some kind of mutually-agreed resolution to the hideously complicated sex web that Itou has spun around himself.
It's a story that is disastrous for basically everybody involved, which I have to admit is a first for harem shows, in my experience at least. Generally these things seem to work out okay for the characters, with no clear "winner"1 but also a lot fewer voyeuristic sex tapes and stabbings. I'm not sure the events portrayed here are "realistic" by any means, but it's interesting to see a show that doesn't insist that this is a desirable situation to be in.
It's also something of a relief to see the instigator of such misery get his comeuppance; harem leads tend to be punished lightly, if at all, so I guess we've got to take Makoto's excessive punishment as something of an attempt at balancing those scales.
I can understand why School Days comes up as a joke in those Reddit threads - it's such a difficult show that nobody could be seriously recommending it in the threads where it's brought up. But I'm very glad I watched it, even if it's not something I could ever suggest anyone else doing.
Note: The title of this post, and the image at the top, are explained on the show's Wikipedia page.
1 I'm not sure it's fair to call the successful girl in a harem show the "winner" as the guy is rarely - if ever - much of a prize.