Anybody who's worked in the US foreign service can tell you that people in charge of protocol are often very polite, very considerate, and very attentive to how their actions and words come across to others. It pays not to annoy diplomats and government officers if you have to work with them day after day, and ask them to do favors for you when interacting with their governments. And most importantly, a protocol officer knows what secrets not to say.
I would never hire somebody like C3PO to be in charge of protocol or even translations. He annoys people. He makes rude comments to Chewbacca, R2D2, and other protocol droids. He whines and complains and blurts out inappropriate statements. He's the kind of blabbermouth who would tell all your family secrets to a Sith Lord or a Hutt gangster. And according to an answer for this question, he was built from scavenged parts on Tatooine.
If all the other protocol droids in the galaxy are as rude as him, no wonder the galaxy is going to war! Everyone's droids would have ruffled the feathers (tentacles, eyestalks, whatever) of half the diplomats in the galaxy. Or maybe he's the only rude droid around because he's a custom made one-off built by a small slave boy to do housework for the slave's mother.
Is there any G-canon evidence of other droids being rude or annoying?