The phrase "no shit Conan" refers to the phrase "no shit Sherlock", but instead of Sherlock it's Conan, the main character from the anime Detective Conan.

This phrase is the weeb version of the "no shit Sherlock".
Normie: Did you know that Conan likes Sherlock Holmes?
Weeb: No shit Conan.
by Karizaki January 3, 2019
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