You go into a bar, see that the dispenser clearly has a Pepsi logo, all the bottles in the fridge are Pepsi, the Coca-Cola logo is nowhere to be seen. You ask for a diet coke. What is the expected reaction where you are, (not the reaction you would like, the reaction you would expect.)?
I think Pepsi and Coke have drilled into bars and restuarants for decades to make it clear to customers which products they carry. It reinforces the brand and opens an establishment up to lawsuits if they serve something different than what the customer ordered. That and waitstaff don’t like be yelled out or miss out on a tip for a misunderstanding as customers are known to be assholes.
Anyone who just serves you a Pepsi is likely new or not trained at all.
I don’t like the wording in the OP, because if I clearly see all of that, I’m not going to order Coke. In fact, I don’t usually specify brand at all, just ask for “a cola”, with the hope that this will just get me whichever one they carry, without having to specify further… though even then, I’ve found that they usually do ask “Is Pepsi OK?”.
Now, I don’t have much firsthand experience with what servers say when someone asks for the wrong brand, but given that they usually ask even when I don’t specify a brand, I imagine that they also do so when the customer asks for the wrong one. Which would be entirely reasonable on their part, because while some customers (like me) don’t care too much, others will get upset if the server brings the wrong one, and might opt for some other flavor if their preferred brand isn’t available, and there’s no sense in needlessly upsetting customers.
Strangely enough, I don’t think I’ve ever been in a restaurant in Switzerland that has Pepsi. It’s either Coke or one of the local (Switzerland or Europe) colas. And I know if I ask for Coke, and the restaurant serves one of the local colas, they will ask. Every time.
I expect the bar would mention it was Pepsi, but I doubt they would on a busy Saturday night. Especially if they have a free soda policy for a designated driver policy, so you’re not paying anyway.
I typically drink Coke, but if I see the dispensers or bottles all say Pepsi, I certainly am not going to ask for a Diet Coke as I would assume they don’t carry any kind of Coke products.
If I am in a place and not sure whether they serve Coke or Pepsi, I will ask for a Coke [or Diet Coke]. If they don’t have it they will usually just ask if Pepsi is okay.
Shortly after WWII a friend of my dad had what you might call a secret shopper position. He would walk into a bar and order a rum and Coca Cola. Sometime while nursing the drink he’d pour down a funnel into a plastic bag a sample then after leaving the bar would seal it, put on a label identifying where it came from, and mail it off to Atlanta.
If analysis showed that it was not Coke, the bar would get a letter.
I can’t imagine any situation where it’s better to give something they didn’t order, rather than ask for clarification.
The situation where I could see it being a bit more complicated is in those places where “coke” is the generic word for soda, and Coca-Cola is available. Then you might want to confirm that they actually want the Coca-Cola and not some other soda. But then I’d bet they’d just say “Coca-Cola?” to confirm.
I also disagree with the OP. There are regions in the United States where “Coke” is the local, generic vernacular for ‘cola,’ just like “Kleenex” is genericized vernacular for a facial tissue. Diet coke would mean a diet cola, irrespective of brand.