One time my dad said to a Japanese waiter a word that meant really close friend and afterwards the… - Feed Post by Whinzer9

One time my dad said to a Japanese waiter a word that meant really close friend and afterwards the waiter started acting really awkwardly. I know my dad was trying to "break the barrier" but how do I explain to him that what he said was really offensive? I already tried telling him that it was a cultural thing but he didn't seem to get it.