A couple of examples include the Rick Roll and the motivational pictures. This site has gotten pretty old, and should die immediately because everything they put out is no longer funny, amirite?
Guy 2: That's fuckin' faggotry shit, yo.
Guy 3: No fuckin' shit.
Aside from this, 4Chan is also where every meme ever came from. Many of the things on 4Chan are horrible things (such as goatse). The very few gems that are actually funny make their way to other places on the internet.
This site is home to many Trolls, who use things like goatse and /That Series/ ("Of Warlords and Pleasures"), and other things that cannot be unseen to terrorize other sites through obscene spam. Most of these things are on /b/, which is basically the armory for Trolls. I recommend that, if you feel the urge to visit 4Chan, you leave any religious beliefs, morals and etcetera behind. Also, please make sure there is nothing nearby for you to kill yourself with, becaue you /will/ lose all hope.
Much like the Fight Club, you do not talk about 4Chan. Not ever.
Guy2: The asshole of the 'net.
Guy2: You really don't want to know, trust me.
Guy1: Yes, I do.
Guy2: Okay then... *brings up 4Chan on laptop*
Guy1: OhmyfuckingGodkillit! No, wait, kill me! There is no hope!