Carlos Maza started posting videos on YouTube, and ran afoul of a guy who reminded him of his high school bullies. He asked YouTube to intervene, and then things got extremely complicated.

Further Reading:

Carlos Maza's video series Strikethrough

Mark Bergen on how toxic videos became more common on YouTube

Megan Farokhmanesh's article about Google's LGBTQ employees and their reaction to the company's policy decisions

Kevin Roose's "The Making of a YouTube Radical"