The game of punching someone (usually a friend) close to you on the arm when you see a ginger.
This sometimes becomes a challenge to see who can spot the most gingers and punch the hardest.
Side effects include bruises and usually being glared at by a ginger.
The punched person may cross their fingers right before being punched and yell "knix!", thus making them immune to a ginger punch. If the person this punches you, even though you crossed your fingers, you may hit them back.

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Gingerpunch is when you instantly respond by punching someone in the face without thinking about it. This is the normal reaction when when a ginger unexpectedly enters one's field of view.