Well, I know for a fact that I'm a cynic. But I wanted to have a definition for it, so I took a peek at the Internet. The sweet Wikipedia had some definition, totally irrelevant of the popular culture, based on some old Greek Philosophy practicing Areté.
Finally I found some interesting matching definitions on wiki.answers.com :
What is the difference between a cynic and an idealist?
A cynic is someone who fails to thrive, who picks apart good ideas and has a tendency to make life boring and miserable for himself and others. They do not see the purpose of success. They do not get excited. They do not understand where the passion of others comes from. Idealists are dreamers of success and have a potential to succeed. They have grand dreams of things they are interested in and work hard to see them come to light. If they fail, they can quite easily become cynics themselves. Many might argue that a cynic is simply an idealist who has experienced failure. In other words, you must first be an idealist before you have the capacity to be cynical.
And also, a few interesting quotes on the subject, which I really enjoyed :
“The cynic is one who never sees a good quality in a man, and never fails to see a bad one. He is the human owl, vigilant in darkness and blind to light, mousing for vermin, and never seeing noble game. The cynic puts all human actions into two classes - openly bad and secretly bad.” Henry Ward Beecher
“A cynic is a man who, when he smells flowers, looks around for a coffin.”
H. L. Mencken
“A cynic is not merely one who reads bitter lessons from the past, he is one who is prematurely disappointed in the future.” Sidney J. Harris
And for the end an example of a cynical statement:
"In the depths of my heart I can’t help being convinced that my dear fellow-men, with a few exceptions, are worthless." Sigmund Freud