What are the most unhinged cartoons in your expert opinion?

The Oblongs was fun.
Drawn Together was awful, but a trashy-yet-fascinating kind of awful, and definitely qualified as unhinged.
oh, and superjail, and squidbillies. 1000%, superjail and squidbillies, someone else should've mentioned these by now, I hate to this day that I can still remember them.
Shit, most of Adult Swim's lineup was either syndicated fox series, anime, or completely fucking duck tits insane.

Drawn Together

Æonflux
Ren & Stimpy (especially the adult stuff)
Metalocalypse

Not a cartoon, but number 1 most unhinged kids' show has to be Boohbah. Everyone involved in the making of this show has to have been on drugs constantly, that's the only explanation I can think of for why this show exists.

You Americans don't know the horrors of Kevin Spencer

Anyone seen “Smiling Friends”, it’s a fever dream of an animated series. Also, Aeon Flux and Ren & Stimpy are two of my all time favorites.

adventure time

Ren and stimpy
- Oh, my beloved ice cream bar! How I love to lick your creamy center!
  [talking to a bar of soap]
  You're not like the others. You like the same things I do. Wax paper... boiled football leather... dog breath!
  We're not hitchhiking anymore! We're riding!
- Was gonna say, some of those close-up shots are not for children
- It's wild how many episodes have been edited or removed from circulation due to their content.
  https://renandstimpy.fandom.com/wiki/List_of_banned/censored_episodes
  
  Where can we get the raw footage! Those episodes were awesome lol
- That one episode where Stimpy births out a fart and has to raise it comes to mind.

Venture Brothers beats them all.
- MECHA SHIVA*
  MECHA SHIVA*
  MECHA SHIVA*
  
  IGNORE ME!
  
  MECHA SHEBA
  https://youtu.be/A3ZuVmWrqV8
  Now I know how Brock feels, having to do all the work while these lammos get top billing.
  Sheeesh!
- Those guys are hilarious. Everyone should buy their DVDs/BluRays and enjoy their commentary (but not on first viewing).
  
  Wandering off topic, but if you can find it, watch the special edition DVD of Buckaroo Banzai.
  There's a special on screen commentary track that makes the movie even funnier. At the start, Buckaroo carries a briefcase into the JetCar. The commentary lets us know that he's got a tunafish sandwich and Einstein's brain with him.

Ren and Stimpy Aeon Flux

[https://www.youtube.com/watch?v=LYs_GCy9PRk](You motherfuckers don't even know Rubik or the metric fucktonnes of 80's drugs that went into making it
- What in the world LMAO.
  I was like "Alright. It's about an inanimate (magical?) object to obviously sell a toy...WHY'S IT SPROUTING LIMBS AND A HEAD?!"
  EDIT: THERE'S A PLAYLIST WITH FULL EPISODES
  Why?! How?! LMAO
  
  A lot of coke was snorted at Hasbro in the 80s. Transformers and Gi Joe made them a mint so they were desperate to milk any toy they already had with a cartoon series
  I cannot stress how vapid and terrible every aspect of this cartoon is. From the fact that Rubik is an alien that does magic to the fact that the main villains of the show are a pair of inept petty thieves just provides nothing but agony
  And I've probably seen every episode at least 7 times
  If you had told child me that this cartoon was going to be something I was legit ashamed to have wasted time on, I would have called you a liar and refused to share any snacks from that point on.

I'm surprised no one has mentioned Rocko's Modern Life yet

Courage the Cowardly Dog is crazy
- I most vividly remember the villains, of course.
  The big purple foot fungus mobsters. "eyyeah, see?"
  The evil barber "Nauuughtyyyyy"
  And of course, Rameses. "Returrrrn the slaaab"
  Special mention: Eustice. "Stupid dog!"
  Such a good show though. The things he did for love.
  I loved that show's premise and core message about confronting fear. He was always terrified and saved the day anyway.
  I just wanted him to finally get a happy little dog existence lol...

Drawn Together
- That was real?? I thought it was some fever dream from when I had chickenpox.

Cow & Chicken / I M Weasel.
- Yeah this is the answer that I came here to see. These definitely belong in this list. Cow & Chicken could be particularly unhinged.
  
  Cow's tantrums and crying gets me every time
- Yeah this show was so weird and off-putting. Watched it every day before school.

-- Ren & Stimpy
-- Ed, Edd and Eddy
-- Cow & Chicken
-- Courage, the Cowardly Dog
-- Animaniacs
- Courage deserves the lead
  https://tenor.com/en-GB/view/courage-jumpscare-violin-girl-from-courage-creepy-violin-girl-jumpscare-gif-14348785
  
  Ren&Stimpy had some gruesome stuff. Courage was more on the horror side.

Happy Tree Friends
- This was a great show, I loved this in my early 20s.

Invader Zim
- Not TV but you could absolutely see how much the creators mental health was struggling if you read through his comic series, Johnny The Homicidal Maniac
- More organs means more human!
- Can't believe I had to scroll down this far to find this one

Freakazoid was unhinged and spastic in a way I haven't seen since

I'm not going to count shows aimed at adult audiences because that feels like cheating (that also includes not listing anime aimed at adults because that doesn't seem like the spirit of the question). Of shows aimed at and easily accessible during their run to children I'm going to say Courage The Cowardly Dog and Invader Zim.
Courage had insane creepy visuals in almost every episode.
Zim wasn't consistently freaky to the point of being notable in every episode, but the ones that were, they were really out there. The show was from the mind of the creator of the Johnny The Homicidal Maniac (which I read as a kid thanks to my interest in Invader Zim) and the show's darker elements are obviously reigned in just enough to get on TV.
- I always always wanted all the JTHM comics as a teen. My parents said absolutely not! What do I have with my adult money? All the comics.
  Jhonen apparently has hypnophobia so, that explains a lot.

Before I’d go to school, at 6am the WB channel played what became my private Disney Afternoon equivalent, which rotated through four shows: Jumanji, Garfield, Sonic the Hedgehog, and— for whatever reason— Roughnecks, the animated Starship Troopers series.
It was rated PG, was produced by Paul Verhoeven, and people fucking died. No idea how it snuck in alongside the tamer stuff, but it very much felt unhinged at the time/someone didn’t vet it for kids.
- That show was SO GOOD.
  I also remember the intro is absolutely awesome, and only recently learned it was a Beethoven composition. There was a neat Microsoft ad that used it too, and I was like "THAT'S THE STARSHIP TROOPERS INTRO!" lol
  I noticed watching the DVDs that it felt oddly toned down in some places and not others, even when the plot would get serious.
  Often their rifles sound really silly-space-lasery and they're aiming weirdly upwards instead of at their targets, for example.
  I loved those early CG shows like this though. Heavy Gear, Voltron (before the excellent Netflix one), Beast Wars...I wonder if Max Steele was any good because I never watched that one for some reason...
- Isn't this the show that gta4 made fun of on It's ingame television?

I'm only aware of Brak as a character on Space Ghost Coast to Coast, but if he has his own show I'm gonna find it!
Also how about the Venture Bros, especially with Patrick Warburton's homicidal Brock Samson.

The Oblongs
- I want a Pickles tattoo so bad!

Salad Fingers https://youtu.be/OWBFKL6H7rI
- The fact that I just had a 12 year old tell me they like rusty spoons last week really messed with my head. She was indeed quoting salad fingers.

Duckman.
FL*CL, which is unhinged but not in a sick leaning manner, it's just really weird.
- FL*CL
  That was a bizarre one. My friend was obsessed with it and I was so freaking confused...
  The airsoft episode was a really fun time though hahaha.
  ...oh geeze didn't his grandpa dress as a nazi for that one or something? Man this is going back like 15+ years I just remember guitars getting pulled out of foreheads and flying irons and a weird live-action moped PoV outro...
  I always thought it would be so damn fun getting an entire neighborhood in on an airsoft game though.
  But I only watched it when that friend was over, because I always had at least one parent home and didn't feel like trying to answer "what the heck are you watching?" LOL

Well, Just You Wait!
The villain often times was portrayed drinking and smoking.
- Nu Pogodi is goated

Aeon Flux (the anime TV series, not the movie)
I want to say it was aired as part of the Def II, teenage audience program slot on BBC2 in the '90s, the original UK home of Ren and Stimpy and The Fresh Prince of Bel Air, but the Wikipedia article for Def II doesn't mention it at all.
Edit: Nope, it was Liquid Television (see reply). Some but not all of MTV's weird programmes ended up on BBC2, sometimes even under the original parent name, like Liquid Television.
- As I recall, aeon flux started in the United States on mtv as part of its "liquid television" block in the early 90s. Back when the station was owned by viacomm, same as Nickelodeon. It shared several voice actors with Rugrats too
  
  Ahh, Liquid Television. Thank you. The other block of odd programmes that ended up on BBC2. It's been a long, long time, so I'm not surprised I mixed them up!

Who Framed Roger Rabbit (though that one was a mix of cartoon and live action, still massively unhinged) and Big Mouth
- That looks... uncomfortable.

How on earth could you leave out the Emmy award winning phenomenon Courage the Cowardly Dog?
That show was unhinged
- I swear this show invented a lot of what we now think of as "analog / internet / creepypasta vibe/aesthetic horror"
  It was so unsettling. The farmhouse was unsettling, the relatively few glimpses we got of the outside world in town was unsettling.
  And yet it was also hilarious. It was so satisfying when Courage would figure out the monster's weakness or lore, and go kick the crap out of it, or Muriel would ignorantly just whack it with a rolling pin and call it a day LOL.
  Something only brilliant cartooning could achieve.
- Return the slab…
- Arguably best cartoon ever made
  
  It was fantastic
- All I remember is the granny

This is definitely an older one, but I would like to add Cow & Chicken! Some of that stuff was pretty wild!

• butt ugly martians
• lazy town
• Tex Avery show
• X-DuckX (one of my favorites - just found out that that’s a French cartoon)
• honorable adult mentions: drawn together, robot chicken, ren&stimpy
- Is lazy town classified as a cartoon? It's certainly in fever dream territory, no argument there.
  
  Yeah sorry - I forgot that Angela Anaconda was cutouts or something like that.
- But Ugly Martians haha

Clone High was not for children, it was on MTV! And the Brak Show was on Adult Swim! also, I feel it should be distinct between 'unhinged but good' and 'unhinged but awful', and also perhaps 'unhinged and awful but wildly entertaining '
- And yet we found each other lol. I realize the waters are slightly muddy but just roll with it

Calabash Brothers ( the original from either the 70s or 80s, can't remember which decade ). Still looking for the series that came after ( and also the 2010s version ) with ENG subtitles just to see how insane they are in comparison.
Original contains death in a couple different ways at least, and some weird scenes like one of the characters losing their powers by essentially having magic strike his eyes or 2 characters that look like minors ( but probably aren't ) getting drunk and passing out off of magically conjured wine.

Ugly Americans, wish they wouldn't have cancelled it. Shit was great

Pop Team Epic (Poputepipikku)

Hokuto No Ken, not because it's particularly unhinged but because in France it was programmed in the morning cartoon segment with dragon ball etc... it was so out of place that the dubbers had an obligation to tone it down in the translations and add jokes and puns.
It went about as well as you would expect, just a layer of absurdist humor on top of the ultra violence and gore...

The Marvelous Misadventures of Flapjack

Ren and Stimpy was already mentioned, and that one is pretty out there. Rocko's Modern Life would be a trailing second place imo. Plenty of innuendos and inappropriate storylines in that cartoon.

Am I tripping or is this Guernica?

Happy Tree Friends ended up on TV? Damn, that's fucked up. It was never meant for children.

I love them all but its like, how did this shit get on TV and then anywhere near children lmao.
The Brak Show was on Adult Swim along with a lot of other cartoons aimed at adults. I seriously doubt Happy Tree Friends was grouped into children's programming, but I only know that from the internet.
Fairly Oddparents & Billy and Mandy both had stuff that might be heavy or scary if you think about it, but the surface level stuff had enough humor involved to make it less intense than it could have been. A lot of shows for kids have more complex stuff that goes over kid's heads.

Unhinged you say?
https://www.dailymotion.com/video/x1t9o4

- Yes!

Untalkative Bunny