Optimal rudeness is the amount that is enjoyable to your supporters (people who dislike who you're responding to or what they said) without swamping the message. Too many insults leave you little chance of convincing someone that they are wrong (if that's your goal) or becomes obviously an attack more than a rebuttal and at least in Lesswrong will get you less status/respect. "too few" insults is when you accord too much respect to people who are badly wrong or to statements that are badly wrong. There are things it's better not to waste time on and it's actually better for the forums to insult them, because it discourages them being taken seriously or being mentioned repeatedly.