turtleback bag Share definition Flag When a child's bookbag is so full that his\her bag ends up acting like a turtle's shell causing slouching and slow movement. Billy Jean:Boy Diana sure has a full backpack Smooth criminal:Yea poor Diana has a turtleback bag turtleback bag by LEOGEO October 16, 2009 0 0 Get merch Get the turtleback bag mug. Buy Now — $32.95 See more merch