Nihilism
-Denial of existence of any basic for knowledge or truth
-Rejection of morality, religion, etc.
The only rule is personnal enjoyement.
I think the pessimism point can be answered with the lack of knowledge of nihilism. Let me elaborate with an example of a discussion.
Person A

o you beleive in God?
Person B: No
Person A: Do you beleive there is a reason for life?
Person B: No, we have no purpose
Person A: So you don't beleive in anything like life, religion and the basics in society?
Person B: I beleive only on my own existence.
Even with this example, I don't think I can't really pinpoint nihilism.