Even though it says comic books, some of these might technically be graphic novels or mangas.
And these are all ones I've personally read, so if you know any that are just as bad or worse, feel free to put 'em in the comment section :)
1. Crossed - Garth Ennis
If any comic book could give the movie A Serbian Film a run for its money it would be this vile, evil bastard.
Of course, anything with Ennis's name attached to it is going to be extremely hardcore f*cked up, and you might feel like you need a shower after reading it. The one thing that stuck with me is the Crossed literally ripping a girl apart while they butt raped both her parents and made them watch.
Nihilistic and cruel as all hell, Nothing is safe in the Crossed universe. Even a poor dolphin gets victimized in very unpleasant ways.
2. Verotika - Various
Glen Danzig's Verotika comics made some of the weirdest and most hardcore erotic/horror comics of the 90s.
At least it did draw some of the top talent at the time, Including Frazetta, who did some Death Dealer comics there!
If you want to see the Joker at his absolute psychotic best (worst????), then this is the graphic novel for you.
Honestly, The Killing joke is a children's comic compared to this.
4. The Boys - Garth Ennis
Another Garth Ennis original and the one he said would out-Preacher the Preacher comic book. The Boys really is dark and hellaciously depraved, but it is supported by a fascinating story and great characters.
And it has one of my favorite covers of all time!
5. Any comic based on the works of Clive Barker
There's a lot of them and I love the all! <3
6. Berserk: The Conviction Arc
Okay, all the arcs in Berserk are extremely f*cked up (especially after the events of the Eclipse) but it is my favorite manga ever. <3
This is the arc where Guts started acting somewhat human again and interacting with other people, and it's also where Griffith stops being the Femto and is reborn so he can walk the human world again but he is still the demon god.
If you don't know what I'm talking about, you really need to read Berserk.
7. The Convent of Hell
This erotic graphic novel is all about evil nuns and one very horny goat devil. One of the highlights has to be when the Vatican sends in their holy special forces squad to kill every damn body.
8. The Young Witches collection
Like Coven from Hell, I bout a bunch of these out of old Heavy Metal magazines. This is the best Euros comic out there; it's even better than anything I ever found in Heavy Metal.
The whole series is epic and just page to page nastiness. The cover to issue #2 was the only non-hardcore thing I could find.
9. Marvel Zombies
Sometimes even Marvel comics gets nasty as hell, and Zombies was the best! I love those comics :)
And there was that time they decided to kill off all their major characters off-panel. But they inexplicably showed a panel of the Blob eating the Wasp.
The Ultimatum storyline was just crazy as hell........
10. Dark Horse Horror Comics
The best of the best of horror comics IMHO.
Some others worth mentioning:
- The Walking Dead
- Ferals from Avatar comics
-Preacher, Of course
- Spider-Man Noir#1, Because the Vulture freaking eats Uncle Ben
- Hard Boiled by Frank Miller. It makes Sin City look very tame
- Devil Man
- Akira in some parts
- The League of Extraordinary Gentlemen, Volume II, Watchman, and pretty much anything else by Alan Moore
- Jeffrey Dahmer: An Unauthorized Biography of a Serial Killer
- From Hell
- The Joker beating the living hell out of Robin in A Death in the Family
- The Killing Joke
- A lot of the Punisher graphic novels
- The Breed
-Satan's sodomy baby (never read this one but heard about it)
That's all I can think of right now