When Rainbow Dash rejected Pinkie Pie, this troper died a little inside.
Pinkie Pie after The Reveal. Not only is she mentally fragile, but she knows exactly how bad it is. She's completely unable to help herself and is convinced that she's damaged beyond repair.
Chapter 21. It's painful seeing Rainbow Dash and Pinkie Pie (to a lesser extent) exchanging verbal barbs with each other, calling each other out on what they did during the story. You wonder for most of the chapter if their formerly strong friendship will survive at all. Turns into a Crowning Moment of Heartwarming when Rainbow Dash refuses to give up on Pinkie as a friend.