This incident happened to my friend in one of the Moscow shops a couple of years ago:

Friend: can I get a pack of "petra lungs"?
Seller: "Petra" No
D: What do you have?
Q: What do you want?
Q: I want "petra lung"
P: "Petra" is not!
Q: So what do you have?
Q: So what do you want?
Q: I really want a package of "petra lungs"...
...