Everyone was a network newbie once. And not everyone has had the benefit
of reading this book. So when someone makes a mistake -- whether it's a
spelling error or a spelling flame, a stupid question or an unnecessarily
long answer -- be kind about it. If it's a minor error, you may not need
to say anything. Even if you feel strongly about it, think twice before
reacting. Having good manners yourself doesn't give you license to correct
everyone else.
If you do decide to inform someone of a mistake, point it out politely,
and preferably by private email rather than in public. Give people the
benefit of the doubt; assume they just don't know any better. And never
be arrogant or self-righteous about it. Just as it's a law of nature that
spelling flames always contain spelling errors, notes pointing out Netiquette
violations are often examples of poor Netiquette.
(Source: Rule 10-- The Core Rules of Netiquette)