I love the responses here by t he obviously uneducated masses that are no doubt millennials and Gen Z pissants that are all entitlement children that never had your asses beat by your parents as you should have been.
1) The establishment is not burger king. They have the right to refuse to modify their menu. Get the fuck over it.
2) The customer said they had a "gluten allergy" which meant that it was utter bullshit and not actual celiac disease. There's a difference. Educate yourselves before continuing to make yourselves look foolish.
3) The establishment is likely what is known as a piano bar and lounge which is more an establishment that is for actual adults to go to for drinks and entertainment but also enjoy a meal knowing that there will be no substitutions or modifications to the menu. Most of the time these establishments actually have rules for dining laid out on their website and actually have a dress code as well.
4) If the customer didn't like the response, they were free to take their cheap, self entitled attitude the fuck elsewhere to some dive and get their meatloaf which is what they actually wanted but for the price of a burger. Instead, they felt the need to run online and post a negative review like the little bitch that they are.
So......bring on the whining and flaming........show me how many WAAAAmbulances need to be called for your generation.