So basically its a lot like Reddit
All I know is that a lot of Hackers use that site.
The warning was supposedly posted on the r9k thread
“r9k/ is a forum dedicated to anonymous sharing of personal anecdotes on the image board site 4chan. The /r9k/ community is most well-known for its greentex.”
4chan is a hipster/script kiddie wannabee place where they pretend alot after getting from the cool kids lunch table. Sometimes come up with funny stuff but mostly just disaffected nerds.