Ok yeah, I worded it a bit badly, I edited the text so it's hopefully more clear.
No Invalidation Gender Identity. Specifically no calling people eggs, also known informally as egging, which is trying to insist that a femboy (or any other GNC person) must be trans due to being GNC
Basically it's saying they must be a girl (trans) because they dress like one. Was a popular thing to do in r/Egg_irl a while back (at the expense of the femboys featured) which is where the term egg came from and why it became known as 'egging'.
Egg - a transgender person that has yet to come out of their "shell".
When a person first makes the realization that they might be transgender, it's referred to as "cracking your egg" in the trans community.
Also, in popular culture it's commonplace to say that a person who is in denial is "putting up walls", so an egg is like a type of wall that completely surrounds you. Cracking your egg involves tearing down those walls.