ninnie Share definition Flag Female version of a Nincumpoop. Someone who is being silly, stupid or without reasonable thoughts. Sarah you big ninnie, you just put your car keys in the ice boxOrIf Beth is a class clown you might say Beth is a ninnie ninnie by ddlD2 April 24, 2014 0 0 Get merch Get the ninnie mug. Buy Now — $32.95 See more merch