I've seen it a few times.
Don't see how it's insulting... 4chan is a wonderful place, /b/rothas!
And of course it comes out of some kind of strange idea that this, yes, this exact forum is "the last bastion of intelligent discussion on the internet" or whatever words they usually use to say it. Of course, a quick look at new/popular posts and the content of such kind of disproves that whole theory, but hey, e-litism doesn't need any proof - it's blind belief.
I mean, come on. This is hardly the worst forum - it's one of the better big-scale forums... But being mistakenly elitist about it is just sad, especially considering how much it contradicts the truth very often.