The complete and utter media black out on a genocide. I got banned from facebook 2 years ago for saying a war with a 1-to-50 casualty rate imbalance was more akin to massacre than a war.

Hmmm. Three-way tie, TBH. I've been on the internet since before Netscape, so take this for what it's worth.

A child (maybe six?) being raped was definitely one of the worst; she was screaming and crying in the brief clip I watched. Apparently it was her father that was raping her; AFAIK he's in prison for life now. Hopefully his life in prison is very short. I'm not even sure how many years ago this was now.

Crush videos involving kittens on an .onion site about a decade ago. I clicked on a thumbnail just long enough to verify that yeah, it was what I thought it was, and then left the site. I've owned cats my whole life; if I knew someone personally that did that, I would absolutely kill them. Yes, I had a stronger visceral reaction to that than I did a child rape video, and no, that doesn't make any sense.

A video from Mexico showing a purported child rapist; he was restrained, and dogs were chewing his genitals off. He had those high, breathy screams of someone in agony that was unable to catch their breath. It ended after the dogs tore his entire lower abdomen to shreds and one of the cartel (?) members cut his throat. Maybe 15 years ago? I'm pretty sure that this was a hi-def video.

I didn't watch the video of the Russian officer cutting the head off a Ukrainian POW. I'm past the point of having any desire to watch videos that further decrease my opinion of humanity.

I saw a group of psychotic cunts cut and eat a piece of someone's heart then laugh at his plea for mercy.

There's plenty, but maybe i put this one near tue top:
Two African terrorists cutting out the heart of a man, while he was alive and awake, giggling and laughing as he slowly moaned to death

Honestly, my answers in specific wouldn't surprise anyone.

If it's fucked up and you could get away with it, at least one person out of 8 billion has done it. Then there's a chance they recorded and published it, and a chance any given person will find it.

The good news is that the other 99.99% of the time things are normal.

Early Facebook days (ares and even Google lmao, tons of common results of those days now are part of the dark net) were wild, not gonna be specific but illegal shit that I didn't even search nor wanted to see

Starting a thread with the equivalent of "You don't have to share your opinion if it makes you or someone else uncomfortable" is the most controversial thing I've seen today at least.

Kekma.org

Don't go there