A misspelling of "Gang Shit". This word has two meanings.
First one is used to describe when someone/something is really cool, mindblowing or funny.
Second one is a name.
I't was discovered by listening to the song bulls on parade by Rage Against the Machine. In the line "With tha sure shot", "sure shot" was mistaken for SHO SHI.
It is a rule that when you hear "sho shi" used, you must scream it