Client emails and asks why a certain element appears on particular page of their website. I respond by saying that they'd asked me to place it there. I then find and forward them the email in which they requested that I place the element on the page. Client replies to forwarded email, "What is this in relation to?".

I must stress that this was all in the space of about two minutes and no other emails were exchanged in-between; there was zero possibility of crossed wires.