In life, we all get to choose how we react to certain situations.
If you have a bad customer service experience, there are appropriate and inappropriate ways to make that known. People who interact with the public have difficult jobs, but they're not always perfect, and sometimes a supervisor needs to know about an employee's behavior. What is absolutely never acceptable is assaulting an employee on the job. And what one dissatisfied bus passenger did to the driver is unthinkable.
Most people would've either just kept it moving or made a backhanded remark.
But not this woman. She had something much nastier in mind.