Also found in: Acronyms.
An initialism of "you must be joking," an expression of disbelief. The initialism is used primarily in text messages and online communications. A: "The boss wants us to come in on Saturday and Sunday." B: "So you're supposed to work 12 days in a row? YMBJ!" A: "This legislation is the worst thing to happen to this country!!!!!!" B: "YMBJ! It's going to help millions of people!!!"
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.