It must be a Fiesta! Share definition Flag Prank intended to disturb tranquility within community groups related to certain high performance vehicles... I've traded in my ecoBoost (Mustang). It must be a Fiesta! It must be a Fiesta! by CoyoteV8 July 26, 2015 0 0 Get merch Get the It must be a Fiesta! mug. Buy Now — $32.95 See more merch