HAHAHA! My boyfriend had someone call him this in a Christmas card and we were bewildered. I finally broke down and looked it up.

“Cotton Headed Ninny Muggins

1) A moron, idiot, dumbass, and overall stupid.

2) A human who accidentally got into santa’s bag, and was raised by elves, who because of his human form, cannot make toys as fast as the elves and is inferior.

3) An inferior toy-maker.

Buddy: “Why don’t you just say it? I’m the worst toy-maker in the world. I’m a Cotton Headed Ninny Muggins.”
Elf: “No Buddy, you’re not a Cotton Headed Ninny Muggins. We all just have different talents, that’s all.”