birdbrain

noun

Etymology: From bird + brain, implying that birds, having small brains, are unintelligent (although this is untrue for many birds).

1. Someone who is not intelligent.

   “That birdbrain just drove right through three rows of traffic cones and into the bushes.”

   “Comedienne Carol Channing, 29, admitted that a grave personal problem had grown out of her playing the role of birdbrained Lorelei Lee in Broadway’s Gentlemen Prefer Blondes. People seemed to be convinced that she is a birdbrain offstage, too: “I won't say that people actually think I’m just two steps removed from outright idiocy, but they do seem to have adopted a protective attitude towards me...””