Here are all my favorite quotes:
Rarity:
Out of all things that could happen, this is THE WORST POSSIBLE THING!
Fluttershy: You're... GOING TO LOVE ME!!!
Twilight Sparkle: I never thought it would happen. My friends... have turned into complete JERKS!
Applejack:
Don't you use your fancy mathematics to muddy the issue!
Rainbow Dash: We tried persuasion, charm, whatever it is Pinkie Pie does...
Pinkie Pie: Hold on to your hooves, I'm about to be BRILLIANT!
Derpy: You okay Rainbow Dash? Anything I can do to help
Rainbow Dash: NO! NOTHING! In the name of Celestia, just sit there and do nothing!
I know I have a lot, but they're all so funny!