I said “have a nice day!” to this old dude and apparently that’s not fucking good enough because he retrieved his wallet and from like a stack of 30 of these things pulled one out and gave it to me and said something like “I hope you reconsider your choices next time”
The English language is something that constantly evolves, and that goes for phrases as well as words. I doubt that when Shakespeare first said “the long and the short of it”, people stopped and told him it’s impossible to tell both the long and short version of a story at the same time unless they are the same story. Or when he coined the term “Love’s Blind” people recalled, disgusted that he could suggest that love, an emotion, is a physical being possible of having some form of disability.
Similarly these phrases have evolved to be shorted. “Have a nice day” is a shortened version of “I hope you have a nice day” to cut out the pronoun “I” as you may say “we” if talking about a group of people or a corporation; it also emphasises how much you would like them to have a nice day, by getting rid of the word hope which suggests there is a possibility of not having a good day; Thus using exaggeration (as they aren’t saying “you must have a nice day”) and removing a pronoun (which focuses on who hopes you have a nice day) it becomes a better phrase, especially in a working environment and thus becomes the more used phrase.
Again, “Have a good one” removes the pronoun so that the person/people wishing you well could be either a person or a group of people. The word “One” is more ambiguous, and thus leaves it open for interpretation by the listener. That way the speaker wishes the well for any thing the listener embarks on. Thus, the speaker wishes the listener well for any and everything, on behalf of himself or any group of people, thus this is also ideal for a work situation (as the message is hopeful and ambiguous) and prevails over similar phrases.
"Not a problem" is a shortened way of saying "there is no need to thank me as the task was not a problem worthy of thanks", because that would be quite the mouthful. Also, phrases such as "my pleasure" or "you’re welcome" imply this was a deal, as if the listener now owes the speaker a favour for having done this task. "Not a problem" shrugs the task off and suggests that this event can be forgotten and that neither of the two are in each other’s debt. Thus as it is a phrase that avoids putting a debt on the listener and is quicker to say than alternatives (again ideal for work situations) is flourishes and prevails.
Thus the evolution of the English Language continues to grow as it must.