Cohn gets into a fight with Jake and Mike because he gets so upset with Jake when he disrespects him.
Explanation:
"The Sun Also Rises" is a novel written by Ernest Hemingway. The story is about Jake's love story.
In chapter 17, Robert Cohn gets into a fight with Jake and Mike when Jake disrespects him. When Cohn asks Jake whereabouts of Brett, and Jake replies rudely and disrespects him. Cohn gets hurt when Jake behaves as this Cohn gets into a fight with Jake and Mike. Cohn, who never brings his athletics outside of the ring, gets into a fight with them.