piranha week Share definition Flag The week before a girl's period (Shark Week) when she wants to ravenously devour everything in site Megan's PMSing and has eaten a whole large pizza and 6 cupcakes. It must be Piranha Week, poor thing. piranha week by Imakeupstuff April 20, 2015 0 0 Get merch Get the piranha week mug. Buy Now — $32.95 See more merch