 Other versions of " have a nice day " are " have a good one " and " have a nice one . " The phrase was universalized after 1950 by truck drivers conversing on their CB radios . Scientific studies indicate that people who regularly smile are more likely to say " have a nice day " . The phrase can have passive – aggressive connotations , and can be caustically used to end transactions with abusive customers . The speaker may also use the phrase ironically , in either a purposeful or unintentional manner . 
