The cat like alien creature that Captain Marvel keeps as a pet. While it may appear as a normal cute Earth cat, inside it's mouth contains a shit ton of tentacles, smaller mouths and even pocket dimensions and bubbles of time.
Rocket Raccoon - *Trying to kill Chewie the Flerken* You have a Flerken on your ship!
Captain Marvel - That's my Cat!
Rocket Raccoon - That is not a "cat"! That is a Flerken!
FlerferFlounce occurs when someone who is a believer in the flat earth theory/hoax joins another conspiracy group based on pictures and hearsay that said conspiracy is real. After being confronted with facts, the person performs a FlerferFlounce, calling people names and leaving the new group.
That new guyjust FlerferFlounced his way out of the group.