An unknown or unidentified illness, often a rash. I think you better get that creeping crud checked out by a doctor—it's not looking so good.
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
1. n. any unidentified disease. There is some kind of creeping-crud between my toes.
2. n. a repellent person. Willy has become such a creeping-crud since he inherited all that money.
3. n. any nasty, slimy substance. That’s not creeping-crud! That’s pecan pie!
McGraw-Hill's Dictionary of American Slang and Colloquial Expressions Copyright © 2006 by The McGraw-Hill Companies, Inc. All rights reserved.