The point of a derail is to shift the conversation of a thread to an unrelated one. There are several examples of this throughout the forum.
Derailing a forum is more difficult but doable. If you had a forum about helping people lose weight, you would derail that forum by having all of the users go off topic and discuss something unrelated. You shift the focus of the intended goal of the forum.
I suspect that the derailing of forums and other things are within the activities of intelligence agencies and other organizations.
This is a supposed leak from operation COINTELPRO. http://pastebin.com/irj4Fyd5
This is to give you an idea of the various operations that has occurred in the past.
It's been known that the Chinese government hires about a million young people to spread propaganda online. They are called the 50 cent brigade. You just had a pro Hillary superpac spent a million bucks to support Hillary Clinton online.
There's clear evidence that various groups around the world are engaged in influencing certain things in the internet.
Derailing a forum would require a catalyst of some kind. A controversy. Something.
Edited 5/6/2016 03:46:04