It's generally considered to be a person of low intelligence and poor personal hygiene and ugly like a dropped pie. A perfect example of a Mong is Isabelle zeva
That dog turd look s like a Mong as in that dog turd basically fits all the criteria to be issabelle zeva
Adj: Someone with absolutely no function in brain ability and no motor skills. Retarded to the highest extent without being wheelchair bound. Retardation breeds in this person, it's the equivalent of cunt in the retard insults.
See also: Mong-Head, Dick-Mong, Mong-Tard, Spas-Mong, Re-Re-Mong.