"Mak ko hijau" is basically a phrase in Malay which is "Emak engkau hijau". In English, its
literally means " Your mother is green". The origin of this phrase was from a video that went viral in Malaysia about
two kids were insults each other in a fight. One of the
kid want to insult but spontaneously said "Mak ko hijau". The reason it became viral at that
time because it is funny. Have you ever heard when some guys or kids mouth fighting each other and suddenly said your mom is green? After it went viral, that is why netizens of Malaysian keep spamming each other "mak ko hijau". It has never been a cursed words but more like
trolling. But when the foreigners talk bad about Malaysia, they gonna get flood of comments saying "your mom is green".