mkcapen1 I love your response regarding Amir's character response, but I also want to add some literary context.
While Amir would absolutely feel this way, we must also consider Hosseini's purpose in having such an unlikely thing happen; in other words, WHY must it be Assef?
The Kite Runner can be considered an epic tale. It investigates heroic feats that better the protagonist and most characters are one-dimensional in the sense that they can easily be distinguished as good or evil. Therefore, while Amir's response is undoubtedly one of shock, fear, and horror, because he understand how despicable this man is, deep down he understand this encounter is necessary for the redemption that he seeks.
I don't know at what point I started laughing, but I did. It hurt to laugh, hurt my jaws, my ribs, my throat. But I was laughing and laughing. And the harder I laughed, the harder he kicked me, punched me, scratched me.
"WHAT'S SO FUNNY?" Assef kept roaring with each blow. His spittle landed in my eye. Sohrab screamed.
"WHAT'S SO FUNNY?" Assef bellowed. Another rib snapped, this time left lower. What was so funny was that, for the first time since the winter of 1975, I felt at peace. I laughed because I saw that, in some hidden nook in a corner of my mind, I'd even been looking forward to this.