Inspired by this.
I was in a Macy’s men’s department looking for a polo-style shirt. The employee had heard of the Polo brand; in fact there was a whole Ralph Lauren section, but no actual classic-style polo shirts for some reason. I didn’t even need a Polo Shirt, just that style of shirt, a soft knit with a collar, short sleeves, and an open neck with 2 or 3 buttons.
Absolutely. No. Idea. What. I. Was. Talking. About.
That’s crazy! I was having trouble once in my local walmart trying to find the Ivory bar soap. I shave it down and use it in the final polish stage for my rock tumbler. Anyway, I was out and needed more, and of course this was when things were first beginning to get scarce. I asked a young store worker stocking nearby if she had any on her cart and could I get a package. She answered with “BAR soap? You want BAR soap? People don’t use that stuff anymore, they use body wash.” and then went on stocking.
So that’s what soapstone is!
I once asked for dried mushrooms at the local grocery store. The little teeny-bopper girl stocking the vegetables had never heard of such a thing, but did point me to the fresh mushrooms. I guess she figured maybe if I let them sit out long enough they’d dry up. 
Another nearby store stocks at least six different varieties of dried mushrooms, including the dried porcini that I usually use for cooking rice and in some gravies. Another store used to give you a choice of either air-dried or sun-dried porcinis, not that I could see much difference. But it’s definitely a cooking staple.
Decades ago, I was in need of an optical disc drive. I went to a computer parts store, and nobody there knew what I was talking about. They said there was No. Such. Thing.
It might also depend on the area. In the tropics, for example, polo shirts are popular in place of T-shirts but when collars are required. I heard that even police units use them in place of regular uniforms.
I was at an local Italian restaurant once, fancy enough to have multiple waiters and squid ink pasta as a specialty, but not fancy enough where you could still order American style pizza by the slice and get a pitcher of beer too.
So I went and ordered a pizza as dine-in with some friends. We get the pizza and it’s excellent except I asked the waiter if he had any parmesan cheese in a shaker. He legitimately acted like I had asked him for something in Russian. “Parmesan cheese? Which cheese is that?” I told him it was the whitish cheese that’s grounded up so it kind of looks like salt you sprinkle on Italian food. He looked at me confused some more until finally something dawned on him and condescendingly he replied “OHHHH… You meant romano cheese!” And brought me a shaker of romano cheese to the table.
And no this wasn’t some actual Italian guy who’s fiercely protective of the legitimate Parmesan trademark, he sounded like he was from the California valley.
I’m wondering if that’s sort of a regional thing - because I’ve heard a lot of people call them golf shirts.
Which is probably also the reason the staff in a pizzeria looked at my cousin like she had two heads when she asked for garlic and red pepper - it was in Wichita.
I remember when you could get Kraft Romano and parm in a wrapped double pack… only difference in the packaging is the romano was in a red cardboard shaker and the parm was in green
I’ll blame the venue for this one: I wanted a USB thumb drive, and the kid at Wal-Mart couldn’t even conceive of it. I literally walked him thru various other types of storage - sim cards, portable hard drives, flash drives, all sorts. But when it came to picturing plugging into a USB port - nope, never heard of it. He even acknowledged that the other types could be plugged into a USB port using an adapter or hub, but directly into the port? No way.
I had to go to Best Buy.
This is now 40 years ago, but when living in Texas, I decided I was in the mood for some gefilte fish. I went into a store whose sign said it was a delicatessen and asked for it, and they didn’t know what it was. So I said it was a kind of Kosher food – and they didn’t know what that was, either.
The guy at Staples didn’t know what a photo mini-printer was.
Recently I went to a store with a large lawn care section and asked where I could find a grass whip. Apparently that doesn’t qualify as incredibly common nowadays because no one had ever heard of such a thing and they don’t carry them.
I’ve never heard of that. 
If it helps I’m 67 and live in the UK…
Would they have known what you were talking about if you had said “CD-ROM drive”?
That doesn’t really surprise me- even in NYC ( and even 40 years ago) there are many “delicatessens” which have nothing in common with a “kosher delicatessen” except that they sell food and the employees wouldn’t necessarily know what gefilte fish is.
I will confess I’ve never heard that term. Is that what is also called a string trimmer or weed whacker? I really like the name grass whip, however-- more punishing!
No, not a power tool; at least, I’ve never seen the term used for one.
At the grocery store a few years ago. Cashier was a teenager and as I place my items, a can of Hormel Chili w/beans and a package of hot dog buns, on the belt she asked if that was all. I said “yep, got the hot dogs at home and going to make chili dogs for supper”. She asked “what are chili dogs?” I explained what they were and she said she never heard of them.
I’m confused too. How do you distinguish a “USB thumb drive” from a “flash drive”? For me, the two terms are synonymous.