Imperative

Yesterday I went to the post office. I asked for eleven stamps and then watched the cashier cutting a receipt and throwing it to the basket. I was afraid that she wouldn't give it to me, mostly because it wasn't for me, and I asked her politely if I could have that receipt."That wasn't yours, don't hurry", she replied. I can't say she was rude, besides I know her, she is good at what she does; but I can assure you, the imperative sounded terrible. So, today's lesson is: avoid using imperative when serving someone. I have to find cases where one should use it. One is certainly when you have to convince or sell something; but never when serving.