What one is said to feel crawling on or under the skin during a drug-induced hallucination. ("Crank" is a slang name for methamphetamine.) I would guess that crank bugs are the reason his arms are all scratched up.
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
n. a drug-induced hallucination that insects are crawling under one’s skin. (Drugs.) There’s no such thing as crank bugs, so stop scratching them.
McGraw-Hill's Dictionary of American Slang and Colloquial Expressions Copyright © 2006 by The McGraw-Hill Companies, Inc. All rights reserved.