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This movie is so incredibly 80s (it came out in 1989), and yet simultaneously, so incredibly timeless. I think of it as a sort of prototype for high school "mean girls" type movies, but it goes so far beyond that; it's a modern classic of the black comedy genre. It has some hilarious lines (which are, like the movie itself, both retro and timeless). It is also incredibly dark and morbid and violent.
Winona Ryder plays Veronica Sawyer, who is a member of a clique at Sherwood, Ohio's Westerburg High School, called the Heathers, because the core of the group is three girls who all happen to be named Heather. The leader is Heather Chandler, who is the most popular (and most hated) girl at school. There's also Heather Duke (Shannen Doherty), who is bulimic and apparently not well respected by Heather #1. And there's Heather McNamara, who is a cheerleader. All the Heathers are mean and snobby and treat most other kids at school like dirt. Veronica doesn't like them or the things they do, but she goes along with it because she enjoys being popular. (There's a cliched and very minor subplot about how Veronica used to be friends with a girl named Betty Finn, whom she abandoned when she got the chance to join the Heathers.)
Anyway, one day Veronica meets a new boy at school, a transfer student named Jason Dean (or "J.D."), played by Christian Slater (at his Jack Nicholson-sounding best). At first J.D. seems pretty cool, basically because he hates the Heathers and the jocks and all the kinds of people Veronica also can't stand. So the two of them start hanging out, and having sex, and whatnot. Then one day, they end up killing Heather #1, which it seems like J.D. wanted to do, but Veronica just wanted to make her sick. Then J.D. has the idea to make it look like a suicide, and gets Veronica to forge a note from Heather.
I should mention the entire movie is pretty surreal. It has an air of complacent normality about it, like even suicide doesn't really phase anyone that much. People just go about their lives. Anyway, there are so many times in the movie that Veronica should realize J.D. is a psychopath, but she doesn't. I mean, not as soon as she should, though she eventually does. He's convinced that she really wants the same things he does, even if she denies it. And I dunno, maybe a part of her did. Maybe he wasn't completely wrong to say that she believed what she wanted to believe. But anyway, there are more murders that Veronica "didn't know" were going to be for real, also made to look like suicides... which actually becomes kind of trendy, so other kids will try to kill themselves.
There are also a number of adults with minor roles... the most notable being Pauline Fleming, who was like a school guidance counselor or something (none of the other teachers took her seriously, thinking of her as a "hippie"). There was also J.D.'s dad, who owned a demolition company (one can kind of see how J.D. became the way he is, because of the way his dad talks as well as a story J.D. tells about his late mother). And there's Veronica's parents, who seem fairly blasť about, you know, everything (though her dad was actually kinda funny). Also there was like a reverend or something, who presided over various funerals, and whose presence in the movie I enjoyed because I liked him in "Beetlejuice" (he played Otho). There were also several other kids of note, including jocks named Kurt and Ram, and a girl named Martha, who was probably the most severely picked-on target of the Heathers.
Anyway, I don't want to give away more of the plot than I have, particularly the climactic scene where Veronica tries to stop J.D. from... but I'm not saying what he was trying to do. No more spoilers! But it was epic. And really, he was pretty charming and cool, as psychopaths go. But Veronica was definitely a lot cooler. And um... yeah, it was just a dark, twisted, clever, surreal, funny, crazy, cool movie, and one with just a glimmer of actual heart, buried under all the madness. But mostly weird.