Have a Nice Day.
First there are the escalating "bigger and better" versions. I suppose these are based on the idea that more must be better. Perhaps people are becoming desensitized to plain old "nice" and need something with more horsepower to impart the same effect. For example we hear "Have a great day," "Have a wonderful day," "Have a terrific day," "Have a fun day," and "Have an awesome day." This last variation seems to be mostly used by fundamentalist christians, who believe "This is the day the Lord hath given us." If the day comes from such an impeccable source it must be "awesome", with the implication that if yours is not awesome there is something suspiciously un-christian about you. There are even variations in this, with "Have a blessed day." being the reigning champion of hyperbole in the bible-belt.
Then there are the blase or laconic variants, such as "have a good one," "have a nice one," etc. These sort of remind me of the old story about how all jokes are numbered, and all you have to do to get a laugh is say "Thirty Eight" and everyone breaks up. The punchline of course is that a newcomer tried saying "Thirty Eight" and no-one laughed. When he asked why, they said: "we've heard that one before." When someone says "Have a good one" they are apparently speaking some kind of shorthand. It is not necessary to ask: "A good what?" But surely this only works in situations where the missing word is so common as to be unnecessary? If I say "I am going to the store to buy a few big ones," you would be justified in asking "a few big what?" But if I say "I'm going home to drink a few cold ones," most people would fill in the blanks with the word "beers". There is is the element of assumed familiarity and shared lifestyle habits. Since it is assumed we all have the habit of wishing each other "a nice day," it becomes unnecessary and un-cool to say the phrase in full.
Then there are the very specific variants. No longer content with a blanket directive covering the entire day, people are slicing time more and more thinly. I have heard "Have a nice morning," "Have a nice afternoon," "Have a nice evening," "Have a nice lunchbreak," etc. Funny thing about "Have a nice evening"... people seem to start using it about noon. Mostly it is store-salespeople and hotel-clerks. Every time I check into a hotel about 2:00, the desk-clerk always finishes by telling me to "have a nice evening." Am I supposed to just skip the afternoon entirely? Either they work in windowless, clockless environments, and have no idea what time it is, or they perceive themselves as imprisoned in the mundane grind of a meaningless job, and for them - life could not possibly begin until one finishes work and goes home ... finally able to "have a nice evening." Wishing that on me is some kind of tacit assumption that I live the same lifestyle.
Then again perhaps every utterance of this type is just a kind of meaningless fluff to fill an otherwise embarassingly blank space. No! Really? Can we really be that insincere? Curiously, almost every Britisher I talk to says Americans seem superficial and insincere compared to English people. When pressed on this point, nearly everyone mentions the phrase "have a nice day" as the prime example of insincerity encountered in the USA. They parrot the phrase with curled lips and dripping sarcasm, as only the British can. It is taken as the de-facto truth in the UK that when any American says these words, he does not really mean them. In fact I looked up the origin of the phrase on a British website, and I found this very unforgiving and anti-American definition ...
Have a nice dayWe might feel a little slighted, but take heart - I've discovered the perfect counter-argument. If you read 'The Canterbury Tales' written in 1387 by English author Geoffrey Chaucer - in 'The Knight's Tale' the character uses the expression "Fare well, have a good day." Chaucer is buried in Westminster Abbey along with Alfred Lord Tennyson, Charles Dickens, and others. He is no literary lightweight. Everything he wrote is studied, revered and idolized in Englit courses worldwide. So if it was good enough for him it should be good enough for his countrymen.
Meaning: A salutation, ostensibly to offer good wishes. In fact a banal and insincere form of words given to anyone and everyone. Evidence of the meaninglessness of the sentiment is the fact that it is even used last thing at night when the opportunity to have a nice day has all but disappeared.
Origin: US origin - around 1970s.
Take that, England! Stop criticizing and go home. And have a nice day.