No shit sherlock is used to insult someone who is stating to blatant obvious. similar to "you don't say" or "thanks captain obvious!"
if someone is saying something obvious instead of saying "no fucking shit" you would add "sherlock" to it just to insult them further.
dude1: hey there is a hole in the boat i think we may sink
dude2: no shit sherlock
29👍 5👎