No one likes to be pre-defined! Even before meeting an IT person, people assume they "get" them. Shows like The IT Crowd lead to misconceptions about information technology.
There are many jobs IT workers specialize in. Of course no one person can do all of these things well, but often they are expected to be a Security Expert, Systems Administrator, Webmaster, Programmer and even Help desk. Too much to be effective.
Here are a few examples of what we thought customers or co-workers think of us and sometimes what we think of them. All in good humor. http://www.orsyp.com/blog/610-sucks-being-it-guy/