"Have a nice day". People still say this, one way or another it betrays loose-stool-water levels of ignorance.
In truth it is increasingly rare now - but if you get a chance I *urge* you to smile and reply:
"Thank you, but I have other plans"
Sadly you must then immediately turn and walk without looking back. Never look back - just have faith that they will be reeling open-mouthed in astonishment. Amen.