Looking up "subjectivism" in the dictionary, I got the following definition:
"The doctrine that all knowledge is limited to experiences by the self, and that transcendent knowledge is impossible."
I cannot envisage how one could possibly get from that to "[a subjectivist] believes himself to be the ultimate ruler of the universe."
This is about moral, not epistemological subjectivism.
Oh, my mistake.
Well, I still think it's kind of a silly statement. Everyone has their own personal set of morals that they then use to run their lives and their interactions with other people. Even if one professes to have received their set from a book, it's still their own interpretation of what was contained there.
I'm not in the crowd who feels that every single set of morals is completely equal to and as good as any other, but I'm also rather wary of professions that one's set of morals is THE set of morals for the universe. The moment a person locks away a certain idea into the box of unquestionability, that person immediately loses the ability to completely and thoroughly think through things, and instead proceeds to try and force the entire world to conform to his or her defined set of unquestionable truths.