I almost refused sale to a customer this morning on the grounds that he was pissing me off.
He bought a Mexican cola and a pack of American Spirits, which are quite expensive at my store ($6.79 USD before tax). I told him his total, and as he's counting his money, proceeds to ask me the individual prices of each item which I told him (less tax). He remarks that the cigarettes are expensive, I just agree. He proceeds to hand me $7.00. I told him, "No, sir, your total is $8.45. You need a $1.45 more."
He says something inaudible about the prices I quoted him.
"No, sir," I respond calmly, but assertively. "I told you the soda is $1.29 before tax, and the cigarettes are $6.79 before tax; with tax, your total comes to $8.45."
He continues to argue, but I make no response, because I'm watching him begrudgingly pull another dollar from his wallet, and count the change from his pocket. But his protests were really beginning to annoy me, if he doesn't agree with the price I'm quoting him then he doesn't have to patronize my store. Simple as that.
If he wasn't quick to pay the difference, I would have simply taken the items off the counter and basically tell him to go fuck himself. But probably not using those words, exactly.