 According to author John <unk> , the tediousness of the phrase is exemplified by employees uttering the words so faintly as to be barely audible . The phrase is occasionally used in an ironic manner when others have been disrespectful or have negatively impacted the speaker . In Detroit , a supermarket started a program to have its cashiers tell every customer to " have a nice day " after completing their transactions . After conducting surveys , they realized that more than half of the customers were unaware of whether the clerk had said the phrase . In addition , a number of customers commented that they despised being told to " have a nice day " . In a 2006 study , researchers at Frankfurt University discovered that people who must smile and say " have a nice day " in their jobs are more prone to illness . Flight attendants , waiters , and call center operators , as well as others who are forced to act cheerfully , are more likely to become depressed . This can lead to decreased immune system function . 
