I love-hated Chinatown because the ending is so damn nihilistic. What are some other entertaining movies that have similar endings?

Lots of spoilers.

Brazil, https://en.m.wikipedia.org/wiki/Brazil_(1985_film)

You are lobotomized and you are happy. Kinda the dream really, I would get one tomorrow if I could be assured of the outcome.

Delicatessen https://en.m.wikipedia.org/wiki/Delicatessen_(1991_film)

You kill the person trying to kill you for meat. Maybe that's happy

Betty Blue

https://en.m.wikipedia.org/wiki/Betty_Blue

You smother with a pillow the only person who understands you after she loses her mind

12 Monkeys https://en.m.wikipedia.org/wiki/12_Monkeys

We are all insane, but least insane wins (loses horribly).

I could go on but you see what my life is like.

narrator- he did go on

Bonus: Apocalyplse Now https://en.m.wikipedia.org/wiki/Apocalypse_Now

You go insane and try to do the right thing to find redemption, to achieve this you kill people

Inception

https://en.m.wikipedia.org/wiki/Inception

You have no idea if you have lost the plot (are living in reality) or not, at the end you don't care.

Older.

Un Chien Andalou.

https://en.m.wikipedia.org/wiki/Un_Chien_Andalou

Buñuel and Dali team up, you rape a young woman, you end up buried in sand on the beach.

The Quiet Earth. https://en.m.wikipedia.org/wiki/The_Quiet_Earth_(film)

You think you are the last man on earth, then you find a chick, you bang her, then she finds a more virulent dude. You let them both die.

ETA: added context. 2nd edit formatting

Betty Blue was such a sad movie. Good film, but heartbreaking.
- It is absolutely devastating, and I wish that was my life at the same time.
  
  Come visit anytime, I'm real fun at parties

Memento. From one perspective it's a happy ending, but ...

Fallen (1998), great movie. Denzel Washington plays a detective hunting a serial killer copy cat but that's just the start. Amazing cast, supernatural storyline, great plot.

I still can't listen to "time is on my side" without thinking of this movie. 10/10 gave me nightmares as a kid
copy cat

Well shit, now I am wondering if that was intentional.

Excellent movie!
- Heh I didn't even think of it till just now...
I had zero knowledge about this movie when I watched it and it really blew me away. I still sometimes think about it today.

The Mist.

Not movies, but Rifters series, Blindsight and Echopraxia by Peter Watts; and Killing Star by Zebrowski and Pellegrino. These will never become movies or TV, they're just too nihilistic and have some extremely heavy themes. Watts especially does not shy away from describing and closely analyzing the psyche of some truly horrible characters in Rifters series.

The Rifters trilogy and Blindsight are also free to download on the authors website. Easily worth taking a look for anyone who enjoys dark themes in their scifi.
blindsight is amazing

Requiem for a Dream (2000), although the ending doesn't exactly come as a surprise.

Grave of the Fireflies (1988), an anime by Studio Ghibli. It begins with the end and since I had kids I cannot watch it anymore.

The Road (2009). I've only read the book and cannot bring myself to watch a movie based on that.

Hamlet (1996) and Titus (1999), both based on plays by Shakespeare, don't end well for anyone.

Nightcrawler (2014) was surprisingly good and Jake Gyllenhaal is very good at being sinister.

Synecdoche, New York (2008) is one of my favorite Kaufman movies with the great Philip Seymour Hoffman.

The White Ribbon (2009) is one of my favorite movies of all time. It depicts life in a small German village just before World War I with a focus on the children.

The Seventh Continent (1989) is from the same director as The White Ribbon, Michael Haneke.

Dancer in the Dark (2000) from Lars von Trier with a great performance by Björk. It really is a lot better than you might think.

Edit: Come and See (1985) is a movie that greatly affected me that should not be missing from this list.

I've also heard good things about Gaspar Noe, but I haven't yet seen anything from him.

Not sure if these count as nihilistic exactly, but some suggestions:

Vertigo
Reservoir Dogs
Crouching Tiger, Hidden Dragon
The Birds
Mulholland Drive
The Wicker Man

Somewhere I have a notebook with scene-by-scene notes on Mulholland Drive. Time loops, alternate universes, fever dream sequences that may be real, throwbacks, lookalikes, detours into madness and fear, all that. Multiple viewings. Full Deep River Ontario shit. (We actually IRL visited that creepy diner in CA. That experience is not recommended. The breakfast is OK. The turkey sandwich is 1000 times not OK.)

For me, every theory regarding the "WTF is happening" aspect falls apart when the old couple from the taxi come creeping out of the blue metallic lock box. Like, everything sort of hangs together with some fuzzy dream logic for me, but then falls apart in the true gossamer of dream fashion. There's sometimes a buggy, I guess.

Top 10 of favorite movies.
- Yeah, it's a wonderful movie, so intricate and elusive. Lynch is a genius.

The Graduate has one of my favorite endings ever.

The shot goes on just a little too long, with each glance missing the other.

It does great at exposing the big event doesn't always lead to happily ever after.

Dr. Strangelove has one of the all-time most-iconic nihilistic movie endings.

There's no fighting here, this is the War Room!

I thought I'd add "Oldboy" in case someone else is using this as a reference. Fits the bill I think.

I think Seven falls in that category.

I haven't seen Chinatown, but feel free to cross-post to !moviesandtv@lemm.ee as well

Vanishing Point

You just reminded me of the vanishing, which is also a fucked up movie OP would like.
- Just make sure to watch the original, not the Hollywood remake, which gives it a happy ending.

The Pledge

Read the book in school. One of the few times I really liked a school book.

It might not be exactly what you're looking for, and it's no where as good a movie as Chinatown, but "Beneath the Planet of the Apes" (https://www.imdb.com/title/tt0065462) definitely ends on a very "down" note. I saw it for the first time a few weeks ago and was kind of blown away by the ending.

A Scanner Darkly has an unhappy ending that I don't want to spoil because it is kind of fucked up.

The 2015 movie Remember. Here's the description from IMDb

With the aid of a fellow Auschwitz survivor and a hand-written letter, an elderly man with dementia goes in search of the person he believes to be responsible for the death of his family in the death camp to kill him himself.

I recommend against reading anything else about it if you think you might watch it

A Simple Plan

Not sure if it qualifies as nihilistic, but Upgrade (2018) definetely has a very unhappy ending