"Have a good one!"
I just love (it) when, for example, I'm in a store checkout line and after paying the cashier I'll hear the parting line "Have a good one!" Now, what exactly is that supposed to mean? Have a good bout with the flu? Have a good b.m.? Have a good visit with your proctologist later on? Or simply have a good day? What? "Yeeeeeeeeeeeeeah, I'll have a good one alright. Same to ya!"