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2.
Efficacious remains after expelling dung from the anus, usually due to a lack of stripe swipe, but often due to ones neglect of erasing the mistake. Can lead to droopy drawers or bung prints.
This food tastes like BUM CRUST! Get it out of my face before I bung print all over you!
by Scahbonie October 13, 2003
 
1.
Originating from Egypt, Bum crust describes the phaecal matter that is not properly wiped from the rectum after excreting phoeses. Consequently, the remaining phaecal matter hardens and becomes entwined within the Pubic hair to form what is known as "BumCrust". See arse biscuits
"Ah shit, we ran out of bog roll, I'm like a bum crust factory!"

-or-

"Uhhhh, there's all bum crust in ma pants, Anyone got Scouring pad?"
by Chris Lawlor June 19, 2004