My head canon for the following is that Twilight has been possessed by King Sombra.
T: Look at what I've got here... *Rainbow Dash struggles to break free of Twilight's magical hold* RD: Twilight! Snap out of it! Sombra is using you! T: No Dash, I feel more free tha I've ever been. Now then, I've always wanted to see a star separation... *Twilight then levels out Rainbow and holds her in place* RD: What are you doing?! T: I'll be sure to say hi to the others for you... *Twilight begins to slowly pull Rainbow's body and limbs taught, causing absolute agony for Rainbow* RD: *Screams in pain* OH CELESTIA!! PLEASE! STOP IT!! IM BEGGING YOU!!!
Dear lord. You've had Twilight Sparkle being sadist towards Rainbow Dash, Rarity being sadist towards Applejack and Fluttershy being sadist towards Pinkie Pie (although Pinkie didn't seem to mind). Whats next, MLP:FIM crossed with the SAW Movies.