My boss is forcing me to be an asshole to customers

When customers return items, I'm supposed to make them feel guilty. She gave me a bunch of lines to use, depending on what minor thing was missing or wrong with the item, and kept walking by to make sure that I was saying them. I never did except once after she caught me and yelled at me. She stood right next to me and I had to force myself to repeat one of her lines to the customer. I didn't say it the right way and the person was confused. I felt ashamed.