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2.
(sometimes hyphenated butt-crust)

n. Hardened fecal matter not cleansed from the anal area. (Usually Vulgar)
Quaid's excessive buttcrust stained his underwear.
by Sudo Nim December 15, 2003
 
1.
The forming of crusty/flaky shit around the ANUS.
Antonio grated his butt crust off into Riley's cereal when he turned away
by Riley && Antonio January 29, 2006