Trying saying this one quickly three times. Numbnuts! Numbnuts! Numbnuts!
In my slightly deranged little mind, I find the word 'numbnuts' to be hilarious. I can't explain why. Perhaps because it just sounds so ridiculous. Seriously, you say it with a straight face. We can look over at Bailey and say: "Hey numbnuts! What's happening? What? Oh, that's right. You've got no nuts. Sorry Man."
Ok, yes, that was mean. Our poor, ever-suffering dog. I promise we don't say that [very frequently]. Anyway, on to the definitions:
Etymology:
numb + nuts
Noun
Singular: numbnuts
Plural: numbnuts
1. (mainly US, slang, derogatory, sometimes jocular) A slow-witted, unresponsive, or inept person (usually male).
Tell numbnuts over there to wake up and pay attention to his work.
2. (US, military, slang, derogatory) A recruit who is unintelligent or difficult to train.
The drill instructor must have called him "numbnuts" fifty times today.
See also (slightly modified):
idiot stupid dumbass jerk fool schmuck dickhead twit nincompoop nerve nitwit jackass goober dunce dummy dunderhead dumb douche dimwit
Sonja here: You MUST click here to watch this hilarious Spelling Bell Video (or just watch the video that I'll post on the blog shortly)
Thanks to Wiktionary and Urban Dictionary for definition assistance.