The life changing difference between "do" and "don't"

Attempting to improve on my ability to craft dialogue, I find myself listening to people more and more, eavesdropping on conversations and taking careful note of a person’s choice of words.

Last week I was in Carvel, waiting to order, when the woman in front of me was handed her root beer float. She looked at it, paused a moment and then asked, “Don’t you mix these up?”

Obviously, the woman was a lunatic to assume that a root beer float should be mixed like a shake. The word float implies that the ice cream should be floating in the root beer, and not spun in like some mutated form of a Dairy Queen Blizzard.

But what I noticed even more was her use of the word don’t instead of the word do. 

Note the difference in tone between the two questions:

Don’t you mix these up?

Do you mix these up?

The use of the word don’t implies accusation. It makes the speaker sound rude, condescending, and annoyed. It’s not a nice way to solicit the desired bit of information from the counterperson.

The use of the word do essentially turns the same question into an honest search for information, with no tone of accusation or annoyance whatsoever.

One simple word change could have made this woman’s ridiculous question at least sound sincere and polite, but instead, she came across as a complete jerk.  

Which undoubtedly she is. 

It's a good thing to keep in mind when writing dialogue. And when speaking to other human beings who don't deserve to be treated poorly.

Small word choices can make a world of difference.   

I was tempted to instruct this woman on her poor word choice but chose instead to remain silent. 

Though I don’t do it often, I am capable of restraint from time to time.