"Have a good one!" Store clerks, bank tellers, and other casual contacts close encounters with a cheery "Have a good one!" I always want to ask (but am too polite to do so), "Have a good WHAT?"
One assumes they mean "Have a good day," but do they really? They could just as easily have said that. It has the same number of words, even containing the same number of letters. So there's no greater expenditure of resources in saying "Have a good day!"
So do they mean have a good ... life, romance, dinner, trip or what? It seems a bit like the one-size-fits-all ball caps that fill the top shelf in my closet. With some fiddling on my part, most of them can actually be worn. But regardless of how well they're adjusted, they never fit as well as one that was properly sized to begin with.