Defective End User: often used by tech support people who are tired of answering what the problem with a computer is when it's something so simple they think anyone should be able to figure it out.
Customer: "Why won't my computer work? I turn on the power and everything!"
Tech: "Have you plugged the monitor into the computer?"
Customer: "Oh, do you have to plug it in to the computer, too?"
Tech to fellow tech: "Another DEU problem"