sopho·mor·on·ic
adj.

sopho·mo·ron
n.

A combination of both sophomoric and moron.

soph·o·mor·ic
adj.
Exhibiting great immaturity and lack of judgment

mo·ron
n.
A stupid person; a dolt.

I prefer this one:
A person of mild mental retardation having a mental age of from 7 to 12 years and generally having communication and social skills enabling some degree of academic or vocational education. The term belongs to a classification system no longer in use and is now considered offensive.

So we gather that a sophomoron would be someone lacking any real intelligence and is very immature. This would be your wide-spread high school jock/prep and many lost college students.

Exhibiting great immaturity and lack of judgment compiled with having a mental age of from 7 to 12 years.