Social Dilemma - How Do You Deal with Shopping Cart Rudeness?

Okay, this happened to me over the weekend, and I have to say, it takes a lot to shut me up, but I was really at a loss for words when this happened.  I was shopping at a local department store, let's say a Mart if you know what I mean.  Anyway, I'm coming out of the store and I have my shopping cart and I'm heading to my car.  Well, as I'm heading up the little incline to my car, I see a young woman, probably in her mid-20's finishing up with her cart, and she just leaves it in the middle of the the parking lot.  So I very nicely say to her...oh would you mind putting that over there in the cart rack, someone might hit it.  And she turns to me and says, "it's none of your business....witch."  Only she doesn't say witch.  I was dumbstruck.  I couldn't believe it.  So I said, I don't know why you're so upset, but it's rude to leave it there, because someone could hit it and you know someone else is going to have to put it back.  And she said, "not my problem, witch." (again, not really witch), and she gets in her car and shows me one of her fingers, and it wasn't the pointer.   So of course, I went and got the cart and put it in the rack, and drove home feeling badly.  I hate those kind of interactions, and I couldn't for the life of me figure out what I could have done differently.  So social dilemma today.  Would you have said anything or would you have just left it alone?  And would you have said something differently to the woman?   It wasn't pretty.   Help me out with this one.  What would you have done?