The KNOCK KNOCK skin was removed from the Rust item store because of a copyright complaint, and was immediately made untradeable and unmarketable. The skin features the words KNOCK KNOCK, which was ripped from the box art of the 2015 movie with the same title featuring Keanu Reeves.
Anyone who was lucky enough to purchase the skin in time may still use it in-game, but it's locked to their Steam accounts and cannot be sold or transferred.
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