TechRepublic published The top ten peeves of a support tech.  Being a person who has done support for well over 10 years, I definitely related to most of the issues raised.  Numbers 3 and 4 are the ones nearest and dearest to my heart.

#3 Users who deny having done anything that may have caused the problem.
This is the "What? Doom is installed on my computer? I have absolutely no idea how that could’ve happened" phenomenon. In one instance, a summer intern from the local university MBA program called the help desk to complain that he couldn’t access the network. A quick survey of his computer revealed that it no longer contained any files beginning with the letter n. The intern vehemently denied having deleted any files whatsoever but eventually confessed that he didn’t have anything to do so thought he’d delete all the files he didn’t recognize. Why he started with the letter n remains a mystery.

#4 Being treated like a user by tech support from another company.
I dread problems that result in a call to the manufacturer’s tech support department. I will experiment, read manuals, Google the error message, and sacrifice chickens on the keyboard before I will call a tech support number for a problem I can’t resolve. My pride simply can’t handle answering the most basic questions: Have you checked that the printer is in fact plugged in and turned on? ARRRGGGH. Get me out of here. Please, please, please, put me straight through to your highest support level because I can guarantee that I have tried everything you are going to suggest at least three times. Oh wait, never mind, the power strip was turned off….

Users become like my children when it comes to owning up to having done something wrong on their computer.  "I didn't do anything" is their favorite phrase when asked.  The fact that their harddrive is full of music that no teenager would be caught dead listening to won't stop them from blaming it on their son or daughter. 

And I love callig up support for some product I am using and talking to a monkey on the other end who is going down his helpdesk script instead of listening to me.  Yeah, I've only been doing this since you were in elementary school, but I am sure that you know better than I do and I should just reboot it one more time just to make sure.  I sometimes wish they had an exam that you could pass that would give you direct access to second and third level support.