Okay, it's not quite client-related but family can be just as bad...
As the household computer whiz, I'm the person that everyone comes yelling to when there's a problem with the computer. So when my brother impatiently tells me that the computers running slow, I look into it. It turns out that there's some spyware on it (because my family never keep their anti-spyware up-to-date) so I download a few extra programs just to make sure all my bases are covered and start a scan with one of them. I then leave the computer to do its thing.
Brother: Why is the computer still slow?
Me: Because it's scanning for spyware that made it slow in the first place.
Brother: *grumbles angrily and leaves because now he can't play his games*
Enter my mom.
Mom: What's going on with the computer?
Me: I'm scanning it for spyware.
Mom: Can I go on it?
Me: Sure but it will be really slow.
Mom: *getting pissed off* Why do you have to install all these programs on it? It just slows everything down.
Me thinking: So...when your computers slow because of spyware, you demand me to fix it, and when I do, you complain because you now can't work on it for 1 hour while you had all day to do so?
Me saying: These programs are necessary for the security of your computer *and proceed to tell her some horror stories but she still doesn't quite understand it*
Why do I even try? I should just let them pay someone else to hear their complaints.
Maybe for a little revenge: when I'm just about ready to move thousands of miles away to live my my fiance...I'll install Linux on their computer >:)