no shit used as a way of confirming or seeking confirmation of the truth of a statement.
☞ An ironic extension of the phrase, used to imply that something is a statement of the obvious, is no shit, Sherlock, invoking the name of the master detective Sherlock Holmes.
2018Observer He told a tech industry conference that he had only recently grasped how much of Britain's commerce is dependent on free flows across the Channel between Dover and Calais. Britain is an island? No shit, Sherlock.