Have a nice day - just who do you think you’re kidding?

Now this really gets my goat - people in stores saying to you "Have a nice Day".

Do they know me? Do they really care what sort of day I've had or will have? Of course they don't! Do they have any idea of what I would consider a "nice day"? Maybe for me, a "nice day" is one when their store is swallowed by an enormous hole in the ground? Maybe it's reading in the paper about a natural disaster somewhere in the world and feeling good because it happed to "them" and not to me? Maybe "a nice day" for me is the upstairs neighbor buying new furniture - all with wheels?
"Have a nice day" is a meaningless phrase used by insipid store personnel because someone once told them that it’s a positive thing to say, that It makes people feel good and, most important, maybe will get them to come back and shop again. I've got news for! Not this grumpy old man!!!!
When I go in a store, all I want to do is wander around, maybe buy something and then leave - quietly, no fuss, no meaningless ceremonies - at most a thank you from them (obviously not from me - I have a reputation to protect). I most decidedly do not need nor want their empty wishes - just leave me alone or I may bite!