Kia is one of Marjane's childhood friends. He helped her bully another kid with some homemade iron knuckles back in the day when torture seemed fun to a child, and he also served in the war while Marjane was away in Vienna. He came back missing both his left leg and his left arm. Marjane has trouble dealing with this severe disability—it's the handicapped elephant in the room, and she wants to address it, but she doesn't want him to have to talk about it either. It makes their reunion difficult.
However Kia, like Marjane, turns to humor to cope. He tells her a bawdy joke about a disabled soldier, and they're able to laugh and chat like they never spent years apart. She says "the only way to bear the unbearable is to laugh at it" (30.69). His story is a testament to the power of humor… and a good dirty joke.