How does Assef treat Amir and Hassan?

As Amir and Hassan make their way to climb their favorite tree, they meet up with a young "sociopath" named Assef and his friends. Assef taunted Hassan for being a Hazara; Assef also had a habit of taunting Ali (Hassan's father), whom he called Babalu. He praised Hitler and then said that he wanted to finish what Hitler started and rid Afghanistan of Hazaras. He called Amir and Baba "a disgrace to Afghanistan" for taking in Hazaras. Just as Assef threatened to punch Amir with his brass knuckles, Hassan pointed his slingshot at the bully and threatened to take out his eye. Assef and his friends retreated, but promised to come back for Amir and Hassan later.