It's 10:10 p.m., and it's 10 minutes after closing. It was a long night and you can see the finish line. Only one more machine to clean and your shift is over. All of a sudden, the all-too-familiar ding of the door opening sends a wave of dread through you. In walk two people ready for you to take their order. Your boss doesn't like turning people away, so you serve them as quickly and painlessly as possible, trying not to undo much of the cleaning you have already done. While yes, sometimes establishments may serve an individual after closing, it's rude to automatically expect them to.
First, there are most likely hours posted on the door. In the age of technology, it is especially easy to find out when an establishment closes. These hours are not a suggestion, they define the time frame when customers are welcome. Next time you're planning on going somewhere for whatever kind of food you're looking for, please check the hours. We're all begging you.
Some may say "well we're paying them, so they should serve us." To expect someone who could potentially be making minimum wage to serve you after hours because "you're paying them" doesn't really make much sense. It's not like when the food is exchanged for the customer all of that money goes directly to the person that served them. Yes, it goes to the business and eventually, some of it makes its way to the employee, but that's not something one should say to an employee if they are annoyed about not being served after hours.
Employees work longer than the five minutes any given individual spends in the store. There are hours of serving, cleaning, preparing, etc. behind (and ahead of) those five minutes. Closing is a long process that can potentially take hours, and delaying or disrupting that process can be very stressful after a long day. I am not saying that everyone that comes in after closing is inconsiderate. There are people who will walk in after close that genuinely do not realize what they did and will be apologetic and/or offer to leave, and there are also people that will be annoyed that they are not being served. If you or someone you know happens to fall in the latter category, please be considerate. At the end of the day (and during it as well), we're humans too.