Someone who believes they always have the answers, a know-it-all. Usually used to insult that person when they make a stupid insight or just repeat what has already been said. Sherlock being a reference to the literary detective sherlock Holmes.

meaning 'well of course dumbass!'
other phrases like this include grass is green

A phrase often used towards someone who states the obvious.

duh.

what you say when someone says something very obvious.

A very sarcastic way of saying: obviosly.
(Sherlock Holmes was a detective in a classic series of books.)

Stating something obvious, this is a sarcastic way of saying "It's very obvious, you can shut up now."

The victim can follow up with "Fuck you Watson" or similar to defend themselves.

A snide response to someone (usually a know it all) who has made a statement that is very obvious using a sarcastic reference to Sherlock Holmes the famous literary detective.

A full of sarcasm phrase used to state what you're saying is obvious.