To add to your verbal arsenal:
jobbernowl (JOB-uh-nowl) noun
A blockhead.[From French jobard (stupid, gullible), from Old French jobe (stupid) + noll (top or crown of the head).]
from Anu Garg (words at wordsmith.org) who will send you a word-a-day if you sign up.
"That he pays not the least regard to the requirements of convention marks him out as either a superior soul or a right down jobbernowl."
Soseki Natsume; I Am a Cat; Tuttle Publishing; 2002.
It's so close to Lewis Carrol's "jabberwocky" that I can't help but think of Alice in Wonderland when I see it, though. And I run the distinct risk of calling someone a jabberwock instead of a jobbernowl.
No worries. I'm sure they'll get the general idea.