The answer to this question can vary depending on the specific laws and regulations of the country or state in which the waiter/waitress is employed, as well as the policies of the particular establishment where they work. Generally, waiters and waitresses are expected to provide service to all customers regardless of their behavior or attitude, and refusing to serve someone solely based on rudeness or meanness may be considered unprofessional or against company policies.
In some places, employment laws may protect workers from hostile or abusive behavior from customers, and employers may be required to take action to ensure the safety and well-being of their employees. However, simply being rude or mean might not be enough to warrant refusing service or taking disciplinary action against the customer, as long as the behavior doesn't cross the line into harassment or discrimination.
If a customer's behavior is particularly aggressive, abusive, or threatening, waiters and waitresses should report the incident to their supervisor or manager, who can handle the situation appropriately and possibly intervene. In cases of ongoing mistreatment by customers, some employers may consider barring certain individuals from the establishment if they consistently exhibit unacceptable behavior.
Ultimately, it is essential for waitstaff to follow their employer's guidelines and handle difficult customers with professionalism and courtesy, even if the customer's behavior is challenging. If there are concerns about specific incidents or policies, it is best for the employee to discuss them with their manager or human resources department to find a resolution.