Hi, In China, byebye is frequently used as transliteration in colloquial Chinese, except for some senior people, or those who live extremely remoted areas. Even a 4 year old Chinese toddler would say byebye, because it is easier to pronounce than Zaijian, the Chinese equvalent. I use it 50% in the daily life. I wonder whether or not Iranians do also frequently say byebye instead of khodahafez, and take it as a load word in Persian like Merci. Thank you!