Also, you know what? Listen to what I'm going to tell you, as in You know something? He's always hated spicy food, or You know what? They're not getting married after all. Both these colloquial expressions are shortenings (Of Do you know something? or Do you know what?) and are used to emphasize the following statement or to introduce a surprising fact or comment. The first dates from the mid-1900s. The variant, from the late 1800s, should not be confused with what do you know or you know .
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.