It's 2018, which means it's time to take this crusty, antiquated "the customer is always right" mentality and stop using it as an excuse to justify rude, entitled, and ignorant behavior. The customer is not king, the customer is not always right, and in fact, the customer should probably just stay in their lane.
The motto, popularized by Harry Selfridge and Marshall Field in the early late 1800s, was originally intended to solidify customer satisfaction as a top priority as well as make sure customers never feel cheated and their complaints are taken seriously. To this end, many businesses are willing to work with its customers on an individual basis to ensure they leave happy and hopefully return. Companies understand that you are paying them with your hard earned money, but customers don't seem to understand that they are tacitly agreeing to abide by the business's rules, processes, and practices.
As someone who has worked in food for multiple years, a customer who believes that they are entitled to certain extras and freebies simply because they paid money and "the customer is always right" is one of the worst types of people. Not only does this imply that they believe that through simply engaging in the act of exchanging currency for goods and services they are somehow more important than everyone else who has also paid money for the same good or service, it also implies you believe it's in an employee's job description to deal with your absurd antics.
It is my belief that the first circle of hell is made up of ignorant customers, possibly sporting the "can I talk to your manager" haircut, demanding that you could or should conduct business a certain way if you just did x, y, or z. Suggesting that something should be simple and not very inconvenient after a service provider has told you otherwise is not only ludicrous, but depending on the field, rude. By telling someone how to do their job, you're suggesting they're either trying to deceive you or that you somehow know how to do their job better than they do. It's easy to say something should be easy when you have no background knowledge or, even if you do, no concept of why or how a company's policies are in place.
For all intents and purposes, the person you are accosting with your heinous attitude and ludicrous demands is, in this instant, the expert. If there was a specific way you wanted something done, I suggest you do one of the following: spend countless hours of your life working honing your skills to get them a level of professionalism that people will pay for, win the lottery so that you can buy an entire corporation and change their policies from the top down, or just do it yourself.
Alternatively, be respectful and mindful of the fact businesses don't have to accommodate you, but choose to out of the goodness of their hearts.