Lines you'll never catch FIM characters crossing

[manic 121]

I was reading through the "Lines you'll never catch FIM Characters saying" thread, and I was thinking, what sorts of actions taken or moral event horizons would the characters be unlikely to cross. As in, if they do this, it'll forever change how we, and other characters, view them? It could be something that would NEVER happen, or it could be something that would take an extreme event to push them across this line, but be within the realm of possibility. Also what might the outcome be?

 

Eg.

 

Applejack outright lies

RD abandons her friends

Fluttershy knowingly hurts an animal

Rarity knowingly hurts Spike

Spike knowingly hurts Rarity

Twilight burns her books

Luna throws a party (j/k)

 

We've already seen some characters come close, like RD has been tempted to abandon her friends for glory, and Pinkamena is what I imagine would result from Pinkie betraying her element. I wonder if it's possible to corrupt or even lose a cutie mark?

 

 

Visual aid below (from google search):

Edited July 20, 2015 by manic

[Castle Bleck 19,401]

 

And in the shadows could an earth-rumbling laughter be heard:

 

https://www.youtube.com/watch?v=xUfNl4bLGEY

[I used to be a stranger 7,994]

I can easily imagine Twilight never crossing the line into the Forbidden Zone.