Its not self-explanitory, it occurs when there is either an incest relationship because they did not spread apart the genes, therefor resulting in a shallow gene pool.
OR when a child is just plain out retarded..
Synonyms for retarded fuckchild
On this page, you will find 30 slang terms related to retarded fuckchild. Some of the top words include: imbred, pretarded, Shorty, Squeezer, behenchod, and 25 more.