Shinonome is a guy who plays by his own rules. He's known and targeted by the student council pretty much for being infamous as an all-around bad influence on all the students. Before he would regularly skip classes or hurt a random bystander.
Now he's controlling himself more and listening to the rules (small steps). He stopped smoking in order to get Yuki's approval since they have always been childhood 'friends' when Yuki was also a troublemaker. But in the end, he's a Jerk With the Heart of Gold because he usually takes care of his friends, Towa and Yuu (and Yuki), but he might often not show it or make it appear as something entirely else. For instance, he knows Yuki's hidden secrets and he's enjoying every minute of Yuki's anguish even though he never intends to reveal their past.