Yiddish

• nebbish

  (Yiddish) a timid unfortunate simpleton.

• schlemiel

  (Yiddish) a dolt who is a habitual bungler.

• schlep

  (Yiddish) an awkward and stupid person.

• schnook

  (Yiddish) a gullible simpleton more to be pitied than despised; "don't be such an apologetic...

Also contains

• sap

  A person who lacks good judgment.

• dullard

  A person who is not very bright; "The economy, stupid!".

• changeling

  A person of subnormal intelligence.

• space cadet

  Someone who seems unable to respond appropriately to reality (as if under the influence...

• subnormal

  A person of less than normal intelligence.

• airhead

  A flighty scatterbrained simpleton; "she's a total airhead"; "every airhead on a big salary...

• twit

  Someone who is regarded as contemptible.

• idiot savant

  Person who is mentally retarded in general but who displays remarkable aptitude in...

• poop

  A stupid foolish person.

• lame

  Someone who doesn't understand what is going on.

• sheep

  A timid defenseless simpleton who is readily preyed upon.

• scatterbrain

  A flighty and disorganized person.

• dimwit

  A stupid incompetent person.

• dingbat

  A silly empty-headed person; "you would be a dingbat even to try it"; "yet here he was with...

• booby

  An ignorant or foolish person.