A saying said upon parting, often by someone who is not an acquaintance: store employees trained to say ''Have a nice day''
The Dictionary of American Slang, Fourth Edition by Barbara Ann Kipfer, PhD. and Robert L. Chapman, Ph.D. Copyright (C) 2007 by HarperCollins Publishers. Cite This Source
Idioms and Phrases with have a nice day
have a nice day
Also,have a good day;have a good one. A cordial goodbye to you. For example, Thanks for the order, have a nice day, or See you next week—have a good day, or The car's ready for you—have a good one. These expressions have become synonymous with a polite farewell. The first originated about 1920 but, like the variants, became widespread only after 1950.