The feeling of physical discomfort without something physical happening to your body, that is usually caused by: second-hand embarrassment, witnessing physical discomfort happening to someone or something else, opinions and acts that you disagree with on a fundamental level and so on.
Watching people get paper cuts makes me cringe.
The 69 jokes are cringe.
Watching that guy get rejected in front of the whole school made me cringe.
Example of a cringe worthy individual: A fedora-wearing misanthrope who also happens to enjoy My Little Pony and always complains about being "forever alone". Sometimes, he carries fake swords and attaches fake furry tails to his pants and walks around in public pretending he is not human. He spends his days browsing 9Gag and talks about memes on his facebook page. He says "lol" out-loud. He is unemployed and lives in his mother's basement. He prides himself in his sense of humor, where his favorite "joke" involves screaming "D'OH!" in a Homer Simpson voice. He often incorporates the french word "Le" prior to nouns in order to make them funnier. For example, I went to le shopping mall and bought myself le fedora. He uses this word because he doesn't know how to be funny so he resorts to stale Reddit jokes.
The Cringe Channel (www.cringechannel.com) is a comedy site full of examples which perfectly exemplify this type of person