For the love of everything, throw a please in. Be nice about it. I'm not a mind reader. And for the most part, remember how fed up I probably am feeling about people at the moment. I don't need you to add to it.
One guy in particular came to mind for that. I got about three or four increased demands in a row, followed by, "You know how to do your job right?"
I got to the end of the transaction, only by digging my nails into my leg, then calling my manager to cover me for a break early. I couldn't take the abuse anymore.