Yep!
Here's one my SMB brothers and sisters will appreciate, and, yes, this actually happened just a couple of weeks ago. However, we see variations all the time:
Client --- "We hired a new person that is related to our secretary's brother's wife's aunt's cousin twice removed. He/She knows A LOT about computers. Anyway, he/she said the server was real slow when they were using it because he/she noticed some errors. So we rebooted in the middle of the afternoon so he/she could run some tweaks and turn off some unnecessary services. Now we can't access our database, and he/she says it's because of some stuff you had installed that caused a bunch of errors and corruptions. We need you to drop everything you're doing and come fix this now because we're closing in 15 minutes and HAVE to have it up by the morning. Oh yeah, we're not paying because he/she says this is YOUR fault."
Me ---- "If I come out there and find that the problem with the server, which was working flawlessly yesterday, is the fault of this person, you will pay for the emergency call. Right?"
Client --- "Oh, yes. Of course, but it's definitely your fault."
On site, me --- "Why did you turn off all the SQL services, anti-virus, and backup services? Why did you unplug one of the network cables from the server?"
New person --- "Well, SQL was slowing down the machine. It was eating up over 16 GB of RAM!

So, there was obviously something going wrong with it. The anti-virus kept popping up when I was trying to download some music program, so I disabled it. The backup services were running CONSTANTLY, so I turned it off because I was just going to set it up to back up to an external hard drive. That's A LOT cheaper than this other service you have set up. I unplugged the other cable because I needed to plug in my macbook."
Me, with the boss in server room. --- "Why is this person in the server room browsing the web on the server?"
Boss --- "We didn't have another computer free, so we thought this would work til we got one ordered from you."
Me

--- "Here's what happened: He/She turned off the SQL services which is how your database works. Without SQL, it's just a big fat cow sitting there on the hard drives. It uses all that RAM because your database should be fast. Also, because it's a server. The rest of the ram is used for other services, but half is allocated to SQL because you want your database to be FAST so productivity is HIGH. The anti-virus is there to keep things from being downloaded. It's locked down like fort knox to prevent users from installing things like weird music programs which have now installed ad-ware on your SERVER. The backup service is expensive because you want to be able to work even if your place burns to the ground. Remember that conversation where you decided it was worth the cost and paid for the entire year up front? The reason there are two network cables in this machine is because one is dedicated to the backup system so we don't saturate the network. This leads into why the service runs a lot of the time. It takes hourly snapshots so you would risk minimal data loss in the event of an issue. Why were you plugging in your macbook instead of using the wireless network like everyone else?"
New person --- "Every time I tried to access perez hilton (or other stupid site), I kept getting an error to contact my administrator because that site isn't allowed."
Me



--- "So, I can fix this, but I have a question or two before I do. Are you going to pay me? Is this person, or anyone else, ever going to be allowed access to the server room again?"
Boss --- "Yes, and definitely not!"
Turned services back on, plugged nic back in, rebooted server. Total time on site: 15 minutes. Invoice: $375. Client loves me again; new person found a "better opportunity" a week later.
So, least favorite phrase: "We hired someone, and they really know computers."