not to appear ignorant, but what is 4chan?
4chan is a imageboard website modeled off the popular Japanese image boards yotsuba and 2chan. Posters are not required to create an account to post and so there is rarely any distinction between posters. Instead, the name "anonymous" appears. There is no way to know a poster's age or gender. Posters en masse are referred to collectively as "anon." There are several topically related boards on the site, but the "/b" board or "random" is most popular and it's frequent posters commonly refer to themselves as "/b tards."
Offensive and politically incorrect language (by almost any standard of sensibility) is commonplace on the boards. The over saturation of profane language however almost seems to non-dimensionalize terms. For instance, the word "fag" is used almost as every other word, but perhaps most often as a suffix. A old poster on the board refers to himself as an "oldfag," and new poster is referred to as a "newfag." This seemingly would label the site as being very hostile to the LGBT community, but ironically homosexuals are no less accepted and even refer to themselves as fagfags.
It's popularity mostly comes from the fact that it is the origin of almost all known web memes and is the origin of much of the web language that is used in pop culture.
As the user created media platform continues to grow and becomes more and more competitive with commercial media, things like 4chan will only grow in popularity. The site is not all hackers and trouble makers. Also, while I do believe that the site is mostly younger posters, the site is more mature in it's content (interpret as you will...).
If you go wandering into the site, don't say I didn't warn you though. There are things you cannot unsee. I go there, and yes, it is amusing. The really obscene stuff is pretty easy to find because people know where to look for it, so it's also pretty easy to avoid.