Well duh! .....That's eighties speak for yes.
I don't remember hearing it in the 80's.
I don't remember using "Duh" in the 80's or 90's. I remember it year ago, but I'm not into a lot of slang.
My favorite words in the 70's were "Can You Dig It" and "Right On".
I remember using it in the late 70s. According to the Merriam-Webster Dictionary, it has been around since 1966.
www.merriam-webster.com/dictionary/duh