Naw, ITT stands for In This Thread. And >>Text is how posters on 4chan quote other posts. For example, a Channer might link to a post and then write ">>Implying x" under the link, meaning that the linked post implies x. Often, this will be the only text in the answer post at all, perhaps accompanied by a picture of an incredulous or stupid face, meaning that the poster thinks the implication is absurd.
The more you know.
I'm really glad I don't visit the 4chan boards.
I don't think I'm quite dumb enough to endure it.
Nah, you just need to be smart enough to be immune to the stupidity.
But it BURNS!
I have become immune to fire through prolonged exposure (mostly in Real Life).
Well, it IS [mind-affecting].
I don't even want to know what that says about the situation.