Just take the expression as a single entity and don't over-analyse by breaking it into its individual words. We know that "well I'll go to the foot of our stair" hasn't got anything to do with stairs, or going anywhere at all. Just think of it as one big word that expresses utter gobsmackedness. I could care less, when you hear someone saying it, doesn't convey that they care quite a lot but that their caring might conceivably drop off, not to me anyway. I don't like it but there it is. Honestly, you really can't fight this stuff. If lots of people say it over a long period of time, then it's standard English. It's fine to say that you don't like it but there's not much point. I mention my hatred of albeit, prior to and on a daily basis only in these threads. They're all standard English and I use them excessively in knowing company with as much sarcasm as a I can muster.