Justin seems like a jerk, he spread a rumor about Hannah for no reason. Justin also seems like a pretty insensitive person, he went out of his way to make the rumor about her, and didn't care of how it affected her. Justin also seems selfish, since he made the rumor for his benefit, and didn't care for anyone else's.
I feel like Justin is the type of character to put himself before anyone else in most situations. I say this because of the way he spread the rumor about Hannah for his own benefit. He also seems like he would be an extrovert and bully, this is because of the way he seemed to treat Hannah, so he probably treats others the same way.
I am on Hannah Baker's list because I spread a rumor about her, this rumor spread around quickly and had a negative impact on Hannah. So, I'm on her list for making a rumor, that was not true even in the slightest.