Your other defense, would be grab a big handful of stuff, and tell her, "I was going to buy all this. But if this is how you feel, I'll take my business somewhere else!"
You'd be amazed how fast they'll change their tune if a big spender walks out with nothing.
There's a Goodwill by me. I used to make out like a bandit getting white shirts and black pants for work. Once I was ready to be rung up, but the girl behind the counter was too busy gaming to notice. This went on for five minutes, when I finally I told her, "Listen, what's more important, my business or your game?"
I've been on both sides of the counter, and the customer is always right. Even if he's a total d-bag.