1. A devious, scheming, and untrustworthy person, group, organization, etc. You're working for Brett Thompson? Watch out—that guy's a slippery customer. Companies like this are slippery customers, coming up with all sorts of elaborate means of getting around regulations.
2. Someone who is difficult or impossible to apprehend or pin down due to their cunning. The notorious criminal has proven to be a slippery customer for police, eluding capture once again.
3. Someone or something that is difficult or tricky to determine or define with certainty. Modern art is often a slippery customer because it defies the boundaries of what a lot of people consider "real" art. What some may consider utterly brilliant others will stare at and wonder why a seven-year-old couldn't have done better.
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
1. Fig. a clever and deceitful customer. Watch out for that guy with the big padded coat. He may snatch something. He's a real slippery customer.
2. Fig. a slippery creature. This little fish is a slippery customer. Get me something to scoop it back into its bowl.
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs. © 2002 by The McGraw-Hill Companies, Inc.