It pretends to host original content but in fact contains re-posted memes and images almost as old of the internet. 9gag and it's band internet thieves post content often stolen off existing sites and watermarked them.
9gag is much like Facebook nowadays and frequently features posts by people who have only just discovered internet memes and frequently miss the point.
David: And I know a retard who thinks he's Batman. What's your point?
God Tier: 4chan
Hero Tier: reddit
Meh Tier: Tumblr
Shit Tier: 9gag
Even worse than that, they try to sell those memes on t-shirts and pins.
tl;dr fuck 9gag.