Other euphemisms for stupidity include:
misologist
(n.) One with a hatred of intellectual effort.
ephemeromorph
(n.) The lowest forms of life, so low that they cannot be otherwise classified.
witling
(n.) Idiot.
excerebrose
(adj.) Having no brain.
micrencephalous
(adj.) Having a small brain.
anoia
(n.) Idiocy.

That's all I can think of for now.