Z is a shorter version of the word “Zoe”, also turned into a nickname for Haitians. The word derived from “Zoe” translates to bones. Haitians created this nickname for themselves describing themselves as a bone, something that is “rough” or “hard to breakdown”.
The forbidden grade that you receive when you know you are a fukking idiot and didn't revise or even listen to anything or anyone and probably have been adopted by a bunch of nonces