'Gart Mistr of Cogemy' (Usually followed by 'All Cogemy is derpiov of fur') is a meme originated from a thread on the SU Wikia in 2016.
On a thread on a user named Amethystkitten's page. It came from a typo during a Rupphire joke on this thread (http://steven-universe.wikia.com/wiki/Thread:546799) in which it said 'Gart' instead of 'Garnet' as an accident. At the end, the creator of the thread, named I-Ship-Stevidot, replied 'Gart Mistr of Cogemy. All Cogemy is derpiov of fur', a reference to two lines that Garnet made:
"Garnet, master of comedy."
"All comedy is derived of fear."
As 'Gart Mistr of Cogemy' is a relatively new meme, there are no known images of it.
I guess, considering all of the other posts, I'll have to say something similiar to:
OH AMYTHISTKITTYCAT CENSORED IT TP PURSUV MEMNE