Rudeness...I'm Over It!

I am writing this on the heels of what started out to be a GREAT day until.... a VERY rude customer came into the store. I love 99% of my customers but man that 1% of the PITA (pain in the ass) ones are enough to make me throw my hands up and say forget it, and walk away from having this store! I really do love most of my customers, most are local, faithful, and we have developed great relationships over the years. My store is unique in that we live in a VERY small town and so here everyone really has to be nice or everyone in town talks about them, including us! Well, today we were busy rearranging the store when this lady who has never been in the store comes in. We, kandice, Lindsey and myself stop what we are doing to help her. We find her what she is looking for and I proceed to the register, this is where things get really ugly! The register was not plugged in, Lindsey had just moved it and was hooking it back up, so I said no problem we can still ring you up. I totalled her bill and by mistake I thought she said she had the change so I opened the cash drawer and gave her $2.00 back well instead she only had the .01 so I when I realized what had happened I said oh excuse me, I apologize I gave you too much change and I went to take the other dollar back. The customer says to me, It's just math, in a very sarcastic tone. I said, excuse me what did you say? She said it's just math, you know the thing that nobody can do anymore because machines do it for you! Can you believe that??????? I was floored, absolutely appalled that she would even say that! I stood there totally shocked and all that I could say was you know what have a super great day! Then of course after she left a million other things I would have loved to have said to her came to my mind like, yeah lady math went right out the door with manners! What I really wanted to do was run after her car and throw her money at her and take my beautiful Thank you cards back and tell her to #%$* off but I didn't I just stood there at the door to my store and thought why the hell do I even bother when customers ( although they are few and far between) act like this. So it begs the question,...what would you have done? How would you have handled it...what would you have said? Here's to hoping that tomorrow is a better day!