Backu shan Share definition Flag is a person who looks good from the back, but when you get to the front they are really ugly! Drunk in a bar I came up from behind to talk to this hottie. When I saw her face damn she was ugly. That is a backu shan! Backu shan by Tricia Millner May 17, 2008 0 0 Get merch Get the Backu shan mug. Buy Now — $32.95 See more merch