By far the most stupid email I ever got was a feedback to a documentation paper that I wrote.

The email's author went on a rant for long paragraphs, suggesting how the content should be structured, written, pictures suggestions ("something like a box with arrows" kind of description) only to realize, I guess in the middle of writing the email, that my approach was much more user friendly, easier to understand and to follow.

So, after this looong rant the email basically ends with "I see what you did there; forget what I wrote before. Cheers."

My brain stopped for that day. It couldn't handle it.