”But How Are We Supposed to Know That???"

Yesterday in Kyoto, Japan, I heard an American voice insistently asking someone how much a particular coin was worth. I could tell he was asking about the 5-yen coin so I told him. He shows me and says "But there's no '5' on it", how can you tell? I pointed out that there is a '5' on it, but written in kanji: 「五円」(example image)

"But how are we supposed to know that?" he asks in a whiny Karen voice.

"Uh, you're in Japan, maybe learn the language.... or look at a guide book".

He walked off shaking his head.