a lot of people try as much as possible not to acknowledge the humanity of service workers, its completely normal for those workers to become numb to the endless stream of jackasses. Even if the next guy coming up does acknowledge them and treat them like a human, its hard to fault any perceived carelessness. Its also not limited to young people, any supermarket I go to has older peole working and you will encounter the same phenomenon. Its the alienation of labor under capitalism.