It's never ok to be rude in a courthouse, library, or archives, no matter how desperately you want your ancestors' records. The best reason for this is that it is simply common courteous to be as polite as you can when attempting to access records. It is one thing to be politely assertive in obtaining materials you know are publicly available. It is another to be demanding and arrogant. Sometimes staff are simply following policy that has been set by someone else--usually their employer.
There's also a selfish motive in being polite--it increases the chance you get what you want. And you never know when you might need to return for additional materials.