The state of mind reached when a usually meek, demure, and gentle person is pushed past their limits of frustration, tolerance, or anger, and lashes out in an uncharacteristic and frightening fit of untrammeled rage.
In the "My Little Pony: Friendship Is Magic" Season One episode entitled "Best Night Ever", kind-hearted pegasus-pony Fluttershy's inability to make friends with Canterlot's local fauna causes her to develop Fluttershychosis and chase the panicked animals into a gala ballroom, her gown and mane all disheveled and dirty, madly screaming, "...you're...going...to LOOOVE MEEEE!!"
by Tim Snortin, Coffeeholic Brony May 10, 2011