Charles Stross is a fairly well-known SF author (that was sarcasm, btw), and he maintains an excellent blog at http://www.antipope.org/charlie/blog-static/ He recently posted this blog entry describing an email conversation he had with a random person asking him...of all things...about his credentials.
Although the blog post mostly revolves around the ludicrous concept of asking a SF author about credentials, I'd like to draw your attention to the incredibly rude tone of the querent's emails. Personally, I feel Mr Stross went far beyond the call of duty in responding more than once.
Here's an exctract from one of the email he received:
Your time is clearly very valuable, as you would rather argue with me over this than simply take a minute or two to state your credentials. Furthermore, I have no need to know the extent of your writings, I simply need to know if you are indeed certified to be considered a credible source on the topic.
Read it in full here: http://www.antipope.org/charlie/blog-static/2011/07/yes-but-what-are-your-credenti.html