I've been meaning to get back to posting "mistake of the day" for a while, and I've got a little extra time today, so why not?
A few years ago, I had a student who was talking about visiting Hawai'i with her husband, and she said, "We went to a supa (スパ)."
I stopped the IC recorder and played it again, and asked, "What's a supa? A supermarket?"
My Japanese isn't perfect, but I passed 日本語能力試験2級 twenty years ago. I know the word スパ in Japanese, but it didn't occur to me that she meant "spa" because she was speaking English.
The mistake, of course, is that the number of syllables is wrong. "Spa" has one syllable, not two. The more general lesson that syllables are important! If your English pronunciation has the wrong number of syllables, it's more likely to be miscommunicated.