I at last have got some time to write some replies.
This person, believes that because there is no God, no purpose, there is nothing right or wrong. Therefore, he can do whatever he wants without for any rational reason, feeling guilty or bad. He would attack a bunch of people to steal their mobiles if he could, because the only experience he can have is his own, and as the money he would get makes him happy, there is no reason not to do it.
He regularly steals from our school canteen, and sees business conmen as his idols. He has told me that he aspires to reach a high level in a company and then siphon off money for all he's worth. These are the brilliant people who get what they want in life without getting into much danger, and are to be respected, according to him.
This is what I meant by nihilism. Simply rejecting any sort of ethics. He has decided that as nothing is better than anything else, he should simply do what comes naturally to him, seeking pleasure for himself. He has admitted that sometimes he gains pleasure from helping other people and does that, but would not help others if it disadvantaged himself.
Now I'll reply to the replies: