Sorry to hear of your experience. I know how you feel and agree with what others have posted. The extreme couponers along with the show have everyone hating anyone with a coupon - and then treating us like dirt. It was an honest mistake and there was no reason for the rudeness on the cashiers part.
I went into Publix recently and after the cashier rung everything up I handed her several coupons. Maybe 5 at most. The bag boy said "Oh God - not coupons. I hate those things." Like I wasn't even standing there and couldn't hear him. The cashier agreed and they went on to have a discussion about how they hated coupons and the people that bring them in - all as I stood there with my two kids waiting for her to ring them up. Nice customer service...