4Chan has various image-sharing bulletin boards, where users post anonymously. Perhaps the most infamous board is the “/b/” board for “random” topics. This board emphasizes “free speech” and “no rules” (with exceptions for child pornography and some other illegal content). In these message boards, users attempt to troll each other and post the most shocking content they can come up with. They also have a history of collectively choosing a target website or community and doing a “raid” where they all try to join and troll and offend the people in that community.
With the ability to remain anonymous, people will most likely post something borderline horrific or something that near violating the policy without any consequences. This also leads to cyberbullying and exposes the personal information of other people without that person knowing.