A misanthrope is a person that hates people. For instance, an old guy who sits on his porch pointing his gun at random passersby whilst cursing humanity could be called a misanthrope.
Of course, there is also the more subtle variety of misanthrope. Perhaps your coworker is extremely short in conversation, and when she does speak seems to do so with disdain, then hurries directly home. This could also be a misanthrope, trying to distance herself from society as much as possible, while still unfortunately being a part of society itself.