Customers can be annoying, but you can't turn them away.
As others have already pointed out, we aren't a business, we don't ask for your money, and we don't get paid. But even if we did, (Hypothetically speaking) customers pay for a product or service, and unless the description on the menu board specifically says "...with a side of 'please oh please tell me all about how I'm a failure of a human being for not getting your order right, or making you wait behind other people, or <insert any self-entitled excuse here>", I absolutely have no qualms about calling a bad customer out for what (s)he is and showing them the door.
"Then you won't have a business" you say? Sure, maybe if I was in the business of taking crap from customers I might agree, but seeing as how most customers aren't douchebags and seeing as how most customers cheer you on as you're kicking the asshat out the door for thinking he's so damn special or that it's okay to be a douchebag,.I'm going to have to respectfully disagree with your assessment.
NOTE: No, I'm not calling you a douchebag or anything. You just mentioned outdated things, so I just wanted to point out that the notion that the "customer is always right" is on that list, as well.