I've seen really gross gore on Tumblr. This was back in 2010 / 2011 when 4Chan and Tumblr were feuding, so a bunch of 4Chan users created accounts and posted gore in every tag imaginable. Ugh.
I'm lucky that I haven't seen anything worse. That's why I don't even CONSIDER using things like the Deep Web.
I've seen some horrific murder videos. Like this one where a guy is decapitated by a chainsaw and the other by a dull knife. Never again...
The 911 call video comment reminds me. I work for an alarm company, and heard this call where a guy (along with his wife) burned to death on the phone after we called him when his alarm went off. His neighbor had set their gas line on fire in hopes of destroying their own home, and ended up blowing up the neighborhood. It was all over the news a few years ago. But yeah, that was probably the worst experience of my life because just seeing the guys account and knowing he was dead was terrifying and sad.