Dear [□ Sir / □ Madam / □ Representative / □ Journalist / □ Idiot],
I know you believe you know a great deal about [□ linguistics / □ children's literature / □ law / □ psychology / □ other (please specify)]
simply because you [□ use language / □ read Harry Potter and Goodnight Moon / □ watch Law & Order / □ have a mind],
or because you've read a newspaper article about [□ the lack of numbers in Pirahã / □ Dumbledore being gay / □ some Supreme Court decision / □ Prozac].
Besides being funny, the letter makes an important point - there is something to these fields. In fact, there is something to most fields, and you could write this letter about any of them.
Depending on the person's attitude, it is either annoying or an interesting opportunity when someone makes a pronouncement that is not just wrong, but wrong in some fundamental way, in a field about which one knows something. I find this happens to me with linguistics a lot, possibly because the combination of "I know something about it" and "People like to comment on it a lot" is so high.