Fart Hard means something that is veryy hard like SO HARD. It describes so muchhhhhhh hard .
If you cant do a thing that seems hard, you say "ITS SO FART HARD!!"
I hope you understand :)
Example:
Student: THIS TEST IS SO FART HARD, I CANT ANSWER IT
Example #2:
GAMER : THIS GAME IS SO FART HARD, I CANT WIN