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To become creased or wrinkled, as of clothing. After sitting for so long in my suit, the pants are starting to crease up.
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
crease something up
to get creases or folds into something that is supposed to be flat; to wrinkle one's clothing. (Very similar to messed up.) You will crease your jacket up if you don't sit up straight. I was sitting so long that I creased up my pants.
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs. © 2002 by The McGraw-Hill Companies, Inc.