"It's a good job you said that in Japanese," she replied (because I had). "What if he overheard you?"
I don't think he would have cared, frankly - his work as a part-time pet shop assistant is hardly a secret - but it got us talking about the way lesser-known languages are sometimes used as a secret code. My teacher's daughter, for example, has been known to make personal remarks about the appearance of people in the street, safe in the knowledge that she won't be "overheard" because she's making them in Japanese.
I can certainly see the appeal of using a language this way, but it's not something an English monoglot can ever do, given how widely English is understood. Even in Japanese it's a risk: who knows whether the person whose big behind you've just dissed may not also be studying for her JLPT1? Even if you're prepared to take the risk with Japanese, what about, say, German or Italian? How obscure would a language have to be for you to be publicly catty in it?
My friend Miho once told me how she and her husband were on a train in central Europe, going to a language conference. The only other person in the compartment was a European man, travelling alone. She and Hiroshi chatted in Japanese, naturally; but when they came to their destination, their companion surprised and (more interestingly) shocked them by making a polite remark in perfect Japanese as they disembarked.
What interests me about the story isn't that Miho was a little retrospectively embarrassed at being understood (though, knowing her, I don't suppose she had been poking fun at their companion), but that she felt quite strongly that the man should have made it clear that he could understand them much earlier. Apparently he felt it too, because later at the conference (where it turned out he too was a delegate) he found her and apologised for not speaking sooner.
To be honest, I find that quite hard to get my head round - but then, it would never occur to me to assume that no one could understand my native tongue.