So I told him how we say hello to others. At first I taught "O ha yo go za i ma su" and "Sa yo u na ra", But the first one is too long to memorize, I changed it to "O ha yo". And I guess the second one isn't more suitable in office, I taught "O tsu ka re" (shorter than "O tsu ka re sa ma de shi ta". I asked him that he must not say this word to any boss and friend.
Anyway, they like Japan. I have to do everything as the good Japanese do. And My English is still poor.