gaijin
A gaijin is a foreigner. It's a word used in Japan, but if you use it outside of Japan, people might think you're weird or just plain stupid.
My gaijin friend used the word in a conversation and got asked, ‘What is that?’
That gaijin tried to explain the term to his family and got laughed at.
I used the word in a text to my friend and got called a gaijin for being a gaijin.