doof
noun. 

as in nerd, dingleberry, dummy; used to described someone in an affectionate but negative manner. 

used in Northern California communities
Older brother: You are such a doof. 

Younger sister: Am not. You're a doof.

Older brother: No you are.

Younger sister: No you are. 

Also: 
Dude, stop charging the line, ya big doof.