One thing that does annoy me is when people have most of the applied knowledge in their head, it's just that they can not be bothered to use that knowledge just to find out a little more in a particulare IT field or subject.
Like i had to spoon feed him information about how my website template (Basic HTML) worked. And here i am thinking "I know your skill level with HTML, surely you should of been able to work this out for yourself"
The other thing that i hate is Ignorance when it comes down to Latest Product will alway be the best. These are the type of people that purchased Windows 95, Me, Xp (pre-SP1a days), Vista instantly thinking that the product that they are going to be better off and that every thing will work the same as it did before.
Oh and for your Mac users out there having a chuckle.... lets not forget System 5 and the early days of System 7 and OSX.
Sadly these people will complain the most too.
And then there is people that really do not know any better when they see the words BETA. They only have the one computer, and they do some thing stupid like installing a Beta Version of Operating System, Service Pack or Internet Explorer. They then complain "OMG, I just ****ed my PC up."
And finally there are the types of people that who you fix there computer. And then about 6 months later, they call you up telling yo that the problem is still there and that the problem was still there ever since i fixed the computer last. Of course, since you did not fix this problem 6 months ago, and they have been using thier computer for the last since months with the same problem, they expect you to fix it for free this time. And this is not just computer. This also covers networks, internet connections, printers and peripherals.
Seriously people. I had a leaking tap and i called the plumber to fix it, and it still continued leaking after he left, would you wait another 6 months before calling him again to let him know that the problem is still there?