Facepalm

I know I complain about this so much, but I HATE coupons. And more importantly the people who have the coupons.
This one woman comes through my line and she hands me these two boxes before I can ring anything through.
"These are only $3.99" She says. I look on the price tag on the item which says they are $4.99.
"So they're a dollar off?" I ask to make sure.
"Yes. They are supposed to be $3.99. I just want to make sure they ring through as $3.99." I knew they weren't going to ring through at that price so I types in the price manually. It showed up on the screen; two items for $3.99.
"All set," I said and carried on with ringing the rest of her items through. At the end of the order she handed me 2 coupons for a dollar off each for those two boxed items. I handed them back to her and said, "I already took the dollar off."
She looked at me and shoved them back in my face, "No, no. I have coupons for them. They were right on the boxes."
"I already took the dollar off," I said, "I put them in manually at $3.99 each, like you said since that was the sale price." The woman sighed and shook her head at me.
"They're supposed to be a dollar off," she said pointing at the coupons, "It says right here."
I tried very hard to keep my voice even as I tried to explain to her. I scrolled all the way back up to the beginning and pointed to the first two items.
"These are the two items. You told me that they were supposed to be $3.99, but the price tag on them said $4.99 so I manually typed them in to be $3.99. See?" I pointed at the screen again. "I already took the dollar off."
"But I have these coupons," she said. FACEPALM.
"I. Already. Took. The. Dollar. Off." I said, absolutely losing my cool. She sighed again and looked at me like I was an idiot. She had this condescending smile on her face like she felt bad I was so stupid. "No no no no no no no. You don't understand. They were supposed to be a dollar off. That's why I have the coupons." I actually started to tear up at this point out of frustration.
"So your saying there is a double sale on this item?" I said sarcastically.
"Maybe," she said.
"Okay," I said with such an attitude, "I'll take an EXTRA dollar off for you if it makes you feel better." I ripped the coupons out of her hand. I knew they wouldn't scan through, but I tried anyways so she would see and hear the error message. After I typed them in, I made a big show about throwing the coupons in the trashcan. This was for affect since later I would have to retrieve them for my folder so my drawer wouldn't be off.
I handed her the receipt and did not say a word.