Duh means "No shit sherlock" and/or "Thank you captain obvious"

A catch all word to describe anything that is basic, uncool or untrendy. According to The New York Times, "cheugy (pronounced chew-gee) can be used, broadly, to describe someone who is out of date or trying too hard."

Things that are cheugy:

The New York Times
PT Cruisers
Goldendoodles

Australians

Addison Rae
White people
Billionaires

The person writing this definition

explained properly by my 3 year old niece to her father.

means "Of course you idiot"

Patently obvious to the most casual observer.

Sound used to imitate a mentally retarded person as an answer to an obvious remark or question. The person using "duh" is thereby sarcastically indicating that he/she is not retarded and the forgoing remark or question is obvious to him/her.

replacement for the sarcastic retort, " No Kidding! "