in part five Justin how does julien bully jack

One day, Justin leaves the Pullman house at the same time as Auggie's friend Jack, and stays with Jack until the bus comes. Jack borrows a dollar from Justin to buy some gum. While Jack is crossing the street, Justin watches as a couple of kids walk by and sneer at Jack. He asks Jack if they are friends of his; Jack says that they are just some jerks from school named Julian, Henry, and Miles. Jack explains the war going that is raging over his friendship with Auggie. Justin advises Jack to tell a teacher about his problems, but Jack refuses. Jack gets on the bus, and as Justin walks to the subway station he spots the three kids again and warns them not to mess with Jack, tapping his fiddle case because he knows that they do not know what is inside.

In Part Five, Justin shows how Julian bullies Jack by noticing the way Julian and his friends mock and sneer at him as he walks by. Justin realizes these kids are from Jack’s school and are part of the conflict over Jack being friends with Auggie. Their behavior makes it clear that Julian tries to intimidate and pressure Jack through teasing and exclusion rather than direct confrontation.

Julian bullies Jack mainly because Jack chooses to be friends with Auggie. Throughout the story, Julian encourages other students to exclude and mock both Auggie and anyone who supports him. He, along with Henry and Miles, gives Jack a hard time and treats him badly because Jack refuses to join their campaign against Auggie.

In Justin's section (Part Five), Justin notices Julian, Henry, and Miles sneering at Jack as he heads to the bus. Jack explains that they are "jerks from school" involved in the conflict over his friendship with Auggie. Their bullying is mostly social bullying—they tease, exclude, and intimidate Jack because of his loyalty to Auggie. Justin is concerned enough that he later warns the boys not to mess with Jack.

So, in Part Five, Julian bullies Jack by mocking and intimidating him and by turning other students against him because Jack remains friends with Auggie.