>

Really? Genuinely curious what part of Japan you hear it in. I lived in Okinawa for 7 years, and didn't hear that word once from a local. Granted, Okinawa is not mainland Japan, but I also visited the mainland several times and never heard it.
Never heard of this word. Heard “Sammie”, but never sando >

Hahaha I was like to say "Sammy is okay though, right?" >

No. No, it is not ok. >

They say this in Japan too because it does mean sandwhich, but if you're in America where it's just sandwhich, people want to be cute and say sammich instead or other ways of saying it.