[steven]

That's interesting! I've never heard that word before (although I don't really go shopping too much... even when I do I don't think I go to a store with any マストアイテムs).

I always find it interesting how there are words/phrases like this that pop up in Japanese. They obviously come from English but aren't actually correct in English. Although someone like yourself, Sashimister, obviously knows the difference, I've talked to many Japanese people who I guess assume those words are straight English.

I've been compiling a list of these words to make a guide for people to use (might make some videos to have pronunciation included). I'm definitely gonna add this one to the list!