Originated from the motion of sliding the back of your hand up your throat and doing a nice littleflick at the end of the whole motion. Also known as fuck you.
Man: "Hey baby, wanna come over my house and bang?"
Woman: "Chin up!"
Term used to assuage a suffering person and encourage them to persist or endure.
To validate and affirm one to press on.
Metaphor to keep one's head up and eyes forward on what lies ahead, opposed to how typically one's gaze tends downward to the ground while in a sullen state.