Where to Start?

I've had a pretty good attitude recently. It's summer, I've had time off, HP is over, and we've been in the slight pre-rush lull.
I'm closing the store and a woman comes up to the register with a bunch of bargain books. We've been having trouble in this area recently--certain register procedures have been causing "shrink," which is a bad, bad thing.
The books aren't ringing up properly. Of course. I void the transaction and reset the register. This takes all of ten seconds and I explain what I'm doing to the woman. She sighs. TEN SECONDS.
I scan the book again and it's incorrect. I pause, look down at the register, and run through the options I have, trying to figure out which will register as shrink and which won't.
"That price isn't correct," she snaps.
Duh. I'm not standing here staring down at the register, fingers poised over the keys, clearly thinking about something, for NO reason. Obviously I have paused this lovely transaction for a purpose.
"Yup, I know," I say distractedly. Should I take a discount allowance or use a price override--no, NO price override, price override causes shrink...oh, wait, I could type in the ISBN and THEN use 199 to capture the number--does that really work?--hmm...that might work best....
My decision made, which took all of five seconds, I finally look up--and find the woman glaring at me. In fact, I'm surprised I'm still alive, because her eyes are crazy eyes.
"You don't need to be hostile."
I don't think I've heard her correctly because...well, hostile is not a way I'd describe myself at that moment. I was in a wonderful mood, I had only a few minutes left at the store, everything was neat and tidy, but I just couldn't understand why the damn bargain stickers hadn't been scanning. Not something I was mad or even irritated about, just curious. Sure, I didn't appreciate her pointing out something I was clearly aware of, but whatever.
"Sorry?" I say.
"Your attitude. You're being hostile."
"I'm sorry," I try to say, but she storms off, stops one of the cafe workers, points me out, and says I should be reported. For what, I have no idea, since ALL I've said is "Yup I know" and "Do you have any discount cards with us?"

Now, a lot of times when stuff like this happens, I have no witnesses. Luckily I had called M down to help me close, and she was standing right there throughout the interaction. And when I turn to her with a WTF look on my face, hers has a similar expression, confirming the fact that this woman was, indeed, ridiculous.

I'm so glad when someone else can confirm an event because some days I literally would believe I was losing my mind. Hostile? Honestly? I might be a bit flip, sometimes possibly monotone, others perhaps a little disinterested, but I have never been hostile.

Now the Red Sox? They make me hostile. Bookstore? Not so much.