An abbreviation for "good character(s)". It refers to a person or persons who is/are extremely interesting. Good characters do not always have to be your friend; as a matter of fact, they are often seen as complete jokes to you and your friends. GC's are usually invited to parties to enhance the quality of the pictures that will be taken and uploaded to facebook.
"Is Eric coming to the party this afternoon? He's such a GC"
"I went to the Berkshire Apartments and hung out with some GC's. I can't wait to show you the pics"
"Joe got his certification as a reverend over the internet. He drinks whiskey every day and believes he's fighting for the Confederacy in the Civil War. GC!"