Just rolls off the tongue nicely
half-wit (hfwt, häf-)
n. Slang
A foolish or stupid person.
half-witted adj.
half-witted·ly adv.
half-witted·ness n.
Thesaurus
1. half-wit - a person of subnormal intelligence
changeling, cretin, idiot, imbecile, moron, retard
mongoloid - a person suffering from Down syndrome (no longer used technically in this sense)
simpleton, simple - a person lacking intelligence or common sense
2. half-wit - a stupid incompetent person
dimwit, doofus, nitwit
colloquialism - a colloquial expression; characteristic of spoken or written communication that seeks to imitate informal speech
simpleton, simple - a person lacking intelligence or common sense