Page 87 — Edge of Morality
There are many ways this COULD be argued (and I have no doubt I'll see many of them in the comments), but the way Rainbow Dash would put it is something like this. "I'm Chaotic Evil, so why should I listen to you about what I can and can't do?"
Transcript:Twilight Sparkle: Rainbow Dash, who chose us over kindred spirits, represents the…
DM: That’s it! This is where I draw the line.
Twilight Sparkle: What?
DM: The Barbarian as the Element of Loyalty? That’s… That’s so absurd I can hardly describe it.
Rainbow Dash: Who says I can’t be?
DM: Excuse me?! You’re Chaotic Evil! You attacked Twilight in the first hour! You’re clearly not bound to the party in any way.
Rainbow Dash: Hey! I picked that because it lets me do whatever stuff I want without anyone else telling me what to do. Yeah, I plan on doing Evil stuff, but I definitely want no hang-ups about authority.
DM: But…
Rainbow Dash: So say, for instance, I decide to stick with this group because I want to. You can argue about it all you want – I’m Chaotic Evil, so I’m not listening.
Applejack: …Did… you just admit that you like this group?
DM: AAAAAAAAAAAAAAAAAAAAAAAAAA-