silly duffer 

Used to describe a retarded mountain goat but can be used to discipline small children

"Oh Dave your child is such a silly duffer"

silly duffer by Dickmyeat September 8, 2015

silly duffer brother 

"silly duffer brother" or "SDB" for short can be used as a noun or adjective to describe an extremely idiotic person (also a nitwit or fool) or an extremely idiotic action.

SDB combines Aussie slang (duffer) and incorporates a reference to the world renowned Duffer Brothers (American twin brothers who write and direct science fiction films, horror films and television shows - including Stranger Things).

Girlfriend: "I can't find my phone again!"
Boyfriend: "It's in your hand you silly duffer brother (SDB)!"

silly duffer brother by Horatio Bumbus July 26, 2017