Verbose
Talks incessantly.  You know exactly what their problem is within the first fifteen seconds of the call, but they are impossible to interrupt.  They will insist on telling you absolutely everything they have done today.  Often tells you their symptoms several times.

Meandering
Similar to verbose, this type of user takes forever to get to the point.  Rather than telling you the symptoms they insist on telling you, in chronological order, everything they have done since arriving at work this morning - just in case it is relevant.

Timid
Too scared to phone the helpdesk themself.  Gets a colleague to call for them.  A game of Chinese Whispers then ensues.

Busy
As above, but the user is "too busy" to call the helpdesk.  Invariably in management or higher, they ask their secretary (who has no details about the problem) to call the helpdesk.  This usually happens while the user is out of earshot, in a meeting, or away from their desk.

This type of user will also ask their secretary to place an "urgent" call for an engineer to visit them, only for them to ask the breathless engineer to come back later because they are "too busy" to have their problem fixed right now.

Elusive
Never at their desk when the engineer visits.  Never tells their colleagues where they are going or when they will be back.  Typically sets a password on their screensaver, so the helpdesk engineer can't try to fix the problem in their absence.  Will often call the helpdesk to complain that the engineer came while they are away, only to be away again when the engineer tries to visit them.  This can carry on ad nauseum.

Vague
Can't tell you what they did before the error occurred.  Can't tell you what the error message was.  Clicked on "OK" or "cancel" to get rid of the error message, but probably can't tell you which.  If they get an unexpected message on their screen they will push buttons at random until it goes away.

Confused
Swears they are logged on when they aren't.  Swears they are typing in the right password when they're not.  Frequently uses the wrong login for the wrong system.  When told that they are trying to do something which will never work, they swear that is how they have always done it.  Against all odds manages to catch the right bus every day to get to work.

Scared
Frightened to touch anything in case they break it.  If something won't switch on, they will call the helpdesk without first checking whether it is plugged in.  Calls the helpdesk whenever they see any error message.  Will probably call if the printer says "out of paper".  When asked to click on the Start button, they will hand the phone over to a colleague who "knows about computers".

Nervous
A mild version of the scared user.  Whenever anything goes wrong with their machine they are convinced it is because they have done something wrong.  Will go into great detail telling you what they did in a totally unrelated program five minutes before the problem occurred.  If they see the message "program has performed an illegal operation" they will panic and call the helpdesk because they think their machine is telling them that they have done something illegal.

Slow
Unable to follow simple instructions over the telephone.  Can never find the icon or menu that they are asked to click on, no matter how big it is.  Frustrated helpdesk staff normally end up sending an engineer out to them because it's quicker.

Uncooperative
Calls the helpdesk already convinced that they need a visit from an engineer.  Will either begrudgingly follow the instructions they are given over the telephone, or will pretend to be slow until the helpdesk person gives in and sends them the engineer they so dearly want to see.

Uncoordinated
Doesn't know left from right.  Takes forever to talk them through any task because they will always manage to click the wrong button at some stage (normally the last stage of the procedure), thus forcing you to start all over again.

Dependant
Has found out the name of the engineer who fixed their problem last time, and now always asks for them by name when they call the helpdesk.  Doesn't want to speak to anybody other than "their" engineer.  Will call the engineer's number directly if they can get it.

Hanger-on
Feels they have spent too long in the telephone queuing system.  When they finally get through they then refuse to get off the phone.  If asked for some information that isn't immediately available they will insist that you stay on the line while they find it, because they "don't want to have to wait in the queue again".  May even put you on hold while they do it.  Oblivious to the fact they are causing a queue themself.

Urgent
Calls with a genuinely urgent problem which has to be fixed immediately.  Normally a victim of Murphy's Law, this user's printer will break down when they need to print an urgent document for the CEO, and their laptop PC will stop working five minutes before an important presentation.  Has an annoying habit of calling at the end of the day just as the engineers are putting on their coats.

"Important"
Easy to distinguish from the urgent caller, this user is convinced they are the most important person in the building.  They think everybody else should wait, and that they should have their problem sorted out immediately – even if an entire floor has lost network connectivity or the CEO is unable to get into the email system. Their real importance is normally inversely proportional to the loudness of their complaints when told they will have to wait their turn.

Impatient
Closely related to the "important" user.  Assumes they are PC Support's only customer.  Cannot understand why they should have to wait for an engineer to visit them.  Calls back after half an hour to ask why the engineer hasn't been to fix their machine yet.  Often complains loudly about how bad the service is.

"Expert"
Has already (wrongly) diagnosed the problem before they call PC Support.  Is certain that any alternative suggestions you offer won't work.  Has often made matters worse by attempting to fix the problem before calling the helpdesk.  Phrase you most enjoy hearing them say:  "That isn't going to...  Oh, it worked".

Fiddler
Closely related to the "expert".  Changes every parameter they can get their hands on.  Deletes files which they mistakenly believe are unimportant.  Their machine is easily identifiable because the Windows desktop has the most hideous combination of colours and fonts you can imagine.  Causes hours of fun because they always manage to find the most obscure parameter that will stop a program working.  Always claims they haven't changed anything.

Victim
Normally sits near the fiddler.  This user returns from holiday to a machine which looks the same as before they left, right up until the point when they switch it on.  Sometimes hard to distinguish from a genuine fiddler because both claim not to have changed anything.

"Perfect"
Convinced they have not made a mistake or changed anything.  Any problem is always the result of PC Support changing something on the server without telling them.  Won't deviate from this opinion even if their machine is never connected to the network.

Argumentative
Contradicts everything the helpdesk tells them, even if you have the information on the screen in front of you.  Doesn't want to admit that they could possibly be wrong.  Will argue about everything.  If told they are being argumentative they will dispute that too.

Email Addict
Calls in the morning because they haven't received any email today.  Convinced there must be a problem with the email server.  Totally incapable of accepting the notion that nobody has sent them anything today.  A test email from the administrator account normally shuts them up.

Upgrade Addict
Owns a PC which behaves perfectly until somebody else in their department gets one which is better.  At this point they will start having repeated problems with their machine.  They will claim the problems can only be corrected by purchasing a new PC (which is better than the new one their colleague has, of course).

Defective Detective
Spots cause-and-effect relationships which aren't there.  If an engineer was in the vicinity earlier, they will claim that the problem with their machine is a result of what he did.  Finds it hard to believe they are wrong, even if the engineer was doing something totally unrelated, such as changing the toner cartridge in a printer.

Unprepared
Never has any information to hand.  Can't tell you their reference number, or who rang to originally report the problem, or what the engineer who visited half an hour ago looked like.  Often calls from a telephone which is nowhere near their computer, and then can't tell you what is currently on their screen because they can't see from there.  Never thinks to write the information down before calling.

Misguided
Unable to handle the notion that there are several different computer systems.  Always refers to everything they log on to as "the system", even if they are logged on to several different systems at the same time, each with a different login name.  Never able to tell you which system they are talking about because in their mind there is only one.

Misinformed
Tries to get their computer to do the impossible, such as writing data to a CD with a CD-ROM drive, or connecting their laptop to the network by plugging it into a power socket.