Some of my favorites (I used to work tech support for Iomega).

1. People who buy a zip drive and have no idea what it does or how to use it. "where's the start button on this things" "it doesn't have a start button, you can access it through the my computer icon on your desktop and backup your important files" "oh, how do I do that?". I had to explain the concept of copy and paste at least 3-4 times a day.

2. People who talk so quietly you have the volume cranked up and smashing the speaker into your ear and they start mumbling. Another great call I had, the guy held a screaming baby up to the phone just about every 3 seconds.

3. We call them Power Users. They explain how they're so smart they are, and they know so much about computers and you ask them open the device manager and they get confused and do the complete oposite of what you ask them do, or start making pointless changes or skip steps you tell them make so you'll never fix it.

4. People who call without being infront of the computer. Why the hell would you call tech support with a computer problem if your nowhere near your computer. One guy called me from a cell phone on the highway saying "I wanted to uninstall your software so I just went into registry and deleted everything that said iomega, now my icons in my computer are wrong". He hung up when I put him on hold to laugh with my supervisor about that one.

That's all I can think of now. I remember when they were training me (a whole week), they kept saying over and over "any customer that has a good experience with tech support is 4x more likely to buy another product from us than one who never had a problem with theirs". Then they put me out on the phones and my supervisors just wanted me to end the calls as soon as possible. That just bothered me.