Guys, the word comes from "mongoloid" just like the British English term "mong". Chicos, proviene de "mongólico" o "mongolo". Used in US as well "Deja de hacer el mónguer, tío."
"Deja de hacer el mónguer, tío."
The origin of the word monguer is not unknown, it comes from mongoose (in its derogatory meaning).
It is a word invented in social networks to be used instead of idiot, imbecile, delayed mental. Its origin is unknown.