Do you want some fries with that?!
Answers: Why do people use this phrase (beside being in a fast food restaurant) in the US?
It's a joke now... fast food restaurants would try to "up-sell" your burger by offering french fries.... it got so common, people started saying it just to be silly.
because fries go with just about everything..... with that being said, it is pretty tough being on a diet when they always ask, do you want fries with that?
It's an often-heard comment associated with McDonald's, but fast food in general, and goes along with the idea that the United States is a "Fast Food Nation".
Additionally, there is a common trend in saying that if one doesn't complete his or her education (some say high school, some say college) that he or she will end up working in fast food and should, thus, hone their use of the phrase, "Do you want fries with that?"
I don't think it's an outrageously common phrase, but it's not exceptionally unordinary, either.
Mainly to increase sales
It usually means that they think you've asked for a lot and want to sarcastically let you know.